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 $187.83   7.153%   $201.2655   $201.27   $201.25   $201.30  
  Purchase #2 $126.35   6.194%   $134.1761   $134.18   $134.20   $134.20  
  Purchase #3 $60.58   12.175%   $67.9556   $67.96   $67.95   $68.00  
  Purchase #4 $148.65   6.522%   $158.345   $158.35   $158.35   $158.30  
  Purchase #5 $184.51   11.362%   $205.474   $205.47   $205.45   $205.50  
  Purchase #6 $84.98   11.366%   $94.6388   $94.64   $94.65   $94.60  
  Purchase #7 $55.40   3.132%   $57.1351   $57.14   $57.15   $57.10  
  7 purchase totals = $848.30       $918.9901   $919.01   $919.00   $919.00