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 $97.65   9.158%   $106.5928   $106.59   $106.60   $106.60  
  Purchase #2 $67.32   11.366%   $74.9716   $74.97   $74.95   $75.00  
  Purchase #3 $87.60   5.635%   $92.5363   $92.54   $92.55   $92.50  
  Purchase #4 $150.27   5.210%   $158.0991   $158.10   $158.10   $158.10  
  Purchase #5 $222.33   6.322%   $236.3857   $236.39   $236.40   $236.40  
  Purchase #6 $190.36   5.250%   $200.3539   $200.35   $200.35   $200.40  
  Purchase #7 $114.98   9.825%   $126.2768   $126.28   $126.30   $126.30  
  7 purchase totals = $930.51       $995.2162   $995.22   $995.25   $995.30