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 $67.39   7.612%   $72.5197   $72.52   $72.50   $72.50  
  Purchase #2 $7.66   3.597%   $7.9355   $7.94   $7.95   $7.90  
  Purchase #3 $243.40   4.352%   $253.9928   $253.99   $254.00   $254.00  
  Purchase #4 $245.81   10.569%   $271.7897   $271.79   $271.80   $271.80  
  Purchase #5 $141.51   7.778%   $152.5166   $152.52   $152.50   $152.50  
  Purchase #6 $33.26   5.186%   $34.9849   $34.98   $35.00   $35.00  
  Purchase #7 $213.26   3.134%   $219.9436   $219.94   $219.95   $219.90  
  7 purchase totals = $952.29       $1,013.6828   $1,013.68   $1,013.70   $1,013.60