Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $141.91   10.382%   $156.6431   $156.64   $156.65   $156.60  
  Purchase #2 $227.91   11.866%   $254.9538   $254.95   $254.95   $255.00  
  Purchase #3 $178.59   11.563%   $199.2404   $199.24   $199.25   $199.20  
  Purchase #4 $201.96   6.591%   $215.2712   $215.27   $215.25   $215.30  
  Purchase #5 $156.26   8.871%   $170.1218   $170.12   $170.10   $170.10  
  Purchase #6 $131.72   10.463%   $145.5019   $145.50   $145.50   $145.50  
  Purchase #7 $115.25   9.809%   $126.5549   $126.55   $126.55   $126.60  
  7 purchase totals = $1,153.60       $1,268.2871   $1,268.27   $1,268.25   $1,268.30