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 $56.29   8.856%   $61.275   $61.28   $61.30   $61.30  
  Purchase #2 $30.92   7.488%   $33.2353   $33.24   $33.25   $33.20  
  Purchase #3 $243.53   3.153%   $251.2085   $251.21   $251.20   $251.20  
  Purchase #4 $124.78   7.500%   $134.1385   $134.14   $134.15   $134.10  
  Purchase #5 $60.65   8.139%   $65.5863   $65.59   $65.60   $65.60  
  Purchase #6 $190.89   4.752%   $199.9611   $199.96   $199.95   $200.00  
  Purchase #7 $166.79   8.105%   $180.3083   $180.31   $180.30   $180.30  
  7 purchase totals = $873.85       $925.7130   $925.73   $925.75   $925.70