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 $144.73   4.417%   $151.1227   $151.12   $151.10   $151.10  
  Purchase #2 $89.55   9.307%   $97.8844   $97.88   $97.90   $97.90  
  Purchase #3 $122.86   6.382%   $130.7009   $130.70   $130.70   $130.70  
  Purchase #4 $227.72   8.619%   $247.3472   $247.35   $247.35   $247.30  
  Purchase #5 $11.31   11.871%   $12.6526   $12.65   $12.65   $12.70  
  Purchase #6 $45.74   12.785%   $51.5879   $51.59   $51.60   $51.60  
  Purchase #7 $58.93   5.516%   $62.1806   $62.18   $62.20   $62.20  
  7 purchase totals = $700.84       $753.4763   $753.47   $753.50   $753.50