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 $58.83   3.754%   $61.0385   $61.04   $61.05   $61.00  
  Purchase #2 $239.81   6.524%   $255.4552   $255.46   $255.45   $255.50  
  Purchase #3 $199.96   13.532%   $227.0186   $227.02   $227.00   $227.00  
  Purchase #4 $101.30   7.389%   $108.7851   $108.79   $108.80   $108.80  
  Purchase #5 $208.35   5.219%   $219.2238   $219.22   $219.20   $219.20  
  Purchase #6 $230.68   11.781%   $257.8564   $257.86   $257.85   $257.90  
  Purchase #7 $116.75   13.352%   $132.3385   $132.34   $132.35   $132.30  
  7 purchase totals = $1,155.68       $1,261.7161   $1,261.73   $1,261.70   $1,261.70