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 $65.57   11.862%   $73.3479   $73.35   $73.35   $73.30  
  Purchase #2 $221.58   9.161%   $241.8789   $241.88   $241.90   $241.90  
  Purchase #3 $69.53   5.662%   $73.4668   $73.47   $73.45   $73.50  
  Purchase #4 $56.82   11.782%   $63.5145   $63.51   $63.50   $63.50  
  Purchase #5 $190.54   6.704%   $203.3138   $203.31   $203.30   $203.30  
  Purchase #6 $116.80   11.299%   $129.9972   $130.00   $130.00   $130.00  
  Purchase #7 $38.46   6.800%   $41.0753   $41.08   $41.10   $41.10  
  7 purchase totals = $759.30       $826.5944   $826.60   $826.60   $826.60