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 $64.66   10.340%   $71.3458   $71.35   $71.35   $71.30  
  Purchase #2 $116.95   7.729%   $125.9891   $125.99   $126.00   $126.00  
  Purchase #3 $93.46   10.109%   $102.9079   $102.91   $102.90   $102.90  
  Purchase #4 $76.94   10.692%   $85.1664   $85.17   $85.15   $85.20  
  Purchase #5 $35.60   5.593%   $37.5911   $37.59   $37.60   $37.60  
  Purchase #6 $133.29   9.290%   $145.6726   $145.67   $145.65   $145.70  
  Purchase #7 $102.84   5.724%   $108.7266   $108.73   $108.75   $108.70  
  7 purchase totals = $623.74       $677.3995   $677.41   $677.40   $677.40