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 $46.99   4.371%   $49.0439   $49.04   $49.05   $49.00  
  Purchase #2 $185.97   4.606%   $194.5358   $194.54   $194.55   $194.50  
  Purchase #3 $110.25   13.300%   $124.9133   $124.91   $124.90   $124.90  
  Purchase #4 $236.74   11.331%   $263.565   $263.57   $263.55   $263.60  
  Purchase #5 $212.63   10.624%   $235.2198   $235.22   $235.20   $235.20  
  Purchase #6 $17.65   12.752%   $19.9007   $19.90   $19.90   $19.90  
  Purchase #7 $229.59   13.583%   $260.7752   $260.78   $260.80   $260.80  
  7 purchase totals = $1,039.82       $1,147.9537   $1,147.96   $1,147.95   $1,147.90