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 $181.55   6.559%   $193.4579   $193.46   $193.45   $193.50  
  Purchase #2 $105.43   3.708%   $109.3393   $109.34   $109.35   $109.30  
  Purchase #3 $66.75   7.809%   $71.9625   $71.96   $71.95   $72.00  
  Purchase #4 $89.87   4.521%   $93.933   $93.93   $93.95   $93.90  
  Purchase #5 $97.35   10.293%   $107.3702   $107.37   $107.35   $107.40  
  Purchase #6 $190.79   8.396%   $206.8087   $206.81   $206.80   $206.80  
  Purchase #7 $156.60   5.348%   $164.975   $164.98   $165.00   $165.00  
  7 purchase totals = $888.34       $947.8466   $947.85   $947.85   $947.90