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 $118.93   10.665%   $131.6139   $131.61   $131.60   $131.60  
  Purchase #2 $216.25   13.480%   $245.4005   $245.40   $245.40   $245.40  
  Purchase #3 $9.53   6.176%   $10.1186   $10.12   $10.10   $10.10  
  Purchase #4 $154.67   8.317%   $167.5339   $167.53   $167.55   $167.50  
  Purchase #5 $183.65   4.214%   $191.389   $191.39   $191.40   $191.40  
  Purchase #6 $188.66   10.370%   $208.224   $208.22   $208.20   $208.20  
  Purchase #7 $202.92   12.835%   $228.9648   $228.96   $228.95   $229.00  
  7 purchase totals = $1,074.61       $1,183.2447   $1,183.23   $1,183.20   $1,183.20