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 $191.63   6.466%   $204.0208   $204.02   $204.00   $204.00  
  Purchase #2 $225.81   11.545%   $251.8798   $251.88   $251.90   $251.90  
  Purchase #3 $213.28   6.846%   $227.8811   $227.88   $227.90   $227.90  
  Purchase #4 $220.25   7.379%   $236.5022   $236.50   $236.50   $236.50  
  Purchase #5 $73.52   10.870%   $81.5116   $81.51   $81.50   $81.50  
  Purchase #6 $145.79   4.597%   $152.492   $152.49   $152.50   $152.50  
  Purchase #7 $58.98   8.864%   $64.208   $64.21   $64.20   $64.20  
  7 purchase totals = $1,129.26       $1,218.4955   $1,218.49   $1,218.50   $1,218.50