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 $92.65   5.323%   $97.5818   $97.58   $97.60   $97.60  
  Purchase #2 $172.78   13.807%   $196.6357   $196.64   $196.65   $196.60  
  Purchase #3 $234.34   12.639%   $263.9582   $263.96   $263.95   $264.00  
  Purchase #4 $220.43   11.725%   $246.2754   $246.28   $246.30   $246.30  
  Purchase #5 $236.32   12.794%   $266.5548   $266.55   $266.55   $266.60  
  Purchase #6 $153.40   4.235%   $159.8965   $159.90   $159.90   $159.90  
  Purchase #7 $28.66   4.196%   $29.8626   $29.86   $29.85   $29.90  
  7 purchase totals = $1,138.58       $1,260.7650   $1,260.77   $1,260.80   $1,260.90