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 $184.76   13.107%   $208.9765   $208.98   $209.00   $209.00  
  Purchase #2 $116.57   11.813%   $130.3404   $130.34   $130.35   $130.30  
  Purchase #3 $17.28   12.634%   $19.4632   $19.46   $19.45   $19.50  
  Purchase #4 $97.66   4.624%   $102.1758   $102.18   $102.20   $102.20  
  Purchase #5 $121.82   9.478%   $133.3661   $133.37   $133.35   $133.40  
  Purchase #6 $211.44   4.590%   $221.1451   $221.15   $221.15   $221.10  
  Purchase #7 $230.69   9.148%   $251.7935   $251.79   $251.80   $251.80  
  7 purchase totals = $980.22       $1,067.2606   $1,067.27   $1,067.30   $1,067.30