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 $206.95   9.661%   $226.9434   $226.94   $226.95   $226.90  
  Purchase #2 $210.91   8.801%   $229.4722   $229.47   $229.45   $229.50  
  Purchase #3 $151.77   8.331%   $164.414   $164.41   $164.40   $164.40  
  Purchase #4 $241.35   6.261%   $256.4609   $256.46   $256.45   $256.50  
  Purchase #5 $220.41   12.394%   $247.7276   $247.73   $247.75   $247.70  
  Purchase #6 $167.67   4.744%   $175.6243   $175.62   $175.60   $175.60  
  Purchase #7 $168.34   5.322%   $177.2991   $177.30   $177.30   $177.30  
  7 purchase totals = $1,367.40       $1,477.9415   $1,477.93   $1,477.90   $1,477.90