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 $58.64   6.269%   $62.3161   $62.32   $62.30   $62.30  
  Purchase #2 $53.54   4.590%   $55.9975   $56.00   $56.00   $56.00  
  Purchase #3 $208.88   9.294%   $228.2933   $228.29   $228.30   $228.30  
  Purchase #4 $166.42   8.326%   $180.2761   $180.28   $180.30   $180.30  
  Purchase #5 $96.43   11.743%   $107.7538   $107.75   $107.75   $107.80  
  Purchase #6 $204.71   5.159%   $215.271   $215.27   $215.25   $215.30  
  Purchase #7 $47.74   13.209%   $54.046   $54.05   $54.05   $54.00  
  7 purchase totals = $836.36       $903.9538   $903.96   $903.95   $904.00