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 $214.57   8.211%   $232.1883   $232.19   $232.20   $232.20  
  Purchase #2 $83.51   13.675%   $94.93   $94.93   $94.95   $94.90  
  Purchase #3 $181.45   5.510%   $191.4479   $191.45   $191.45   $191.40  
  Purchase #4 $36.26   4.208%   $37.7858   $37.79   $37.80   $37.80  
  Purchase #5 $185.60   13.399%   $210.4685   $210.47   $210.45   $210.50  
  Purchase #6 $69.71   3.586%   $72.2098   $72.21   $72.20   $72.20  
  Purchase #7 $24.76   4.842%   $25.9589   $25.96   $25.95   $26.00  
  7 purchase totals = $795.86       $864.9892   $865.00   $865.00   $865.00