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 $235.27   3.159%   $242.7022   $242.70   $242.70   $242.70  
  Purchase #2 $119.69   5.256%   $125.9809   $125.98   $126.00   $126.00  
  Purchase #3 $21.92   12.263%   $24.608   $24.61   $24.60   $24.60  
  Purchase #4 $220.80   12.268%   $247.8877   $247.89   $247.90   $247.90  
  Purchase #5 $44.79   8.456%   $48.5774   $48.58   $48.60   $48.60  
  Purchase #6 $196.74   9.392%   $215.2178   $215.22   $215.20   $215.20  
  Purchase #7 $67.46   10.579%   $74.5966   $74.60   $74.60   $74.60  
  7 purchase totals = $906.67       $979.5706   $979.58   $979.60   $979.60