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 $242.91   4.562%   $253.9916   $253.99   $254.00   $254.00  
  Purchase #2 $58.55   13.714%   $66.5795   $66.58   $66.60   $66.60  
  Purchase #3 $195.53   7.638%   $210.4646   $210.46   $210.45   $210.50  
  Purchase #4 $158.67   6.794%   $169.45   $169.45   $169.45   $169.50  
  Purchase #5 $138.72   8.612%   $150.6666   $150.67   $150.65   $150.70  
  Purchase #6 $80.52   8.802%   $87.6074   $87.61   $87.60   $87.60  
  Purchase #7 $144.37   13.186%   $163.4066   $163.41   $163.40   $163.40  
  7 purchase totals = $1,019.27       $1,102.1663   $1,102.17   $1,102.15   $1,102.30