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 $47.77   11.151%   $53.0968   $53.10   $53.10   $53.10  
  Purchase #2 $193.96   9.793%   $212.9545   $212.95   $212.95   $213.00  
  Purchase #3 $153.54   3.694%   $159.2118   $159.21   $159.20   $159.20  
  Purchase #4 $48.33   5.780%   $51.1235   $51.12   $51.10   $51.10  
  Purchase #5 $233.72   4.300%   $243.77   $243.77   $243.75   $243.80  
  Purchase #6 $112.43   7.606%   $120.9814   $120.98   $121.00   $121.00  
  Purchase #7 $164.46   11.420%   $183.2413   $183.24   $183.25   $183.20  
  7 purchase totals = $954.21       $1,024.3793   $1,024.37   $1,024.35   $1,024.40