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 $148.41   12.491%   $166.9479   $166.95   $166.95   $166.90  
  Purchase #2 $37.46   8.819%   $40.7636   $40.76   $40.75   $40.80  
  Purchase #3 $171.81   4.782%   $180.026   $180.03   $180.05   $180.00  
  Purchase #4 $15.68   7.634%   $16.877   $16.88   $16.90   $16.90  
  Purchase #5 $168.40   3.114%   $173.644   $173.64   $173.65   $173.60  
  Purchase #6 $57.67   8.358%   $62.4901   $62.49   $62.50   $62.50  
  Purchase #7 $11.96   10.507%   $13.2166   $13.22   $13.20   $13.20  
  7 purchase totals = $611.39       $653.9652   $653.97   $654.00   $653.90