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 $48.51   9.177%   $52.9618   $52.96   $52.95   $53.00  
  Purchase #2 $215.60   13.593%   $244.9065   $244.91   $244.90   $244.90  
  Purchase #3 $110.67   3.159%   $114.1661   $114.17   $114.15   $114.20  
  Purchase #4 $55.61   6.310%   $59.119   $59.12   $59.10   $59.10  
  Purchase #5 $124.64   7.507%   $133.9967   $134.00   $134.00   $134.00  
  Purchase #6 $202.79   6.454%   $215.8781   $215.88   $215.90   $215.90  
  Purchase #7 $40.82   5.615%   $43.112   $43.11   $43.10   $43.10  
  7 purchase totals = $798.64       $864.1402   $864.15   $864.10   $864.20