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 $95.47   13.378%   $108.242   $108.24   $108.25   $108.20  
  Purchase #2 $200.42   3.597%   $207.6291   $207.63   $207.65   $207.60  
  Purchase #3 $52.82   12.229%   $59.2794   $59.28   $59.30   $59.30  
  Purchase #4 $240.59   5.837%   $254.6332   $254.63   $254.65   $254.60  
  Purchase #5 $107.39   12.491%   $120.8041   $120.80   $120.80   $120.80  
  Purchase #6 $16.45   4.269%   $17.1523   $17.15   $17.15   $17.20  
  Purchase #7 $200.56   12.606%   $225.8426   $225.84   $225.85   $225.80  
  7 purchase totals = $913.70       $993.5827   $993.57   $993.65   $993.50