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 $91.36   5.122%   $96.0395   $96.04   $96.05   $96.00  
  Purchase #2 $134.43   7.634%   $144.6924   $144.69   $144.70   $144.70  
  Purchase #3 $178.96   10.779%   $198.2501   $198.25   $198.25   $198.30  
  Purchase #4 $39.54   13.640%   $44.9333   $44.93   $44.95   $44.90  
  Purchase #5 $69.78   9.370%   $76.3184   $76.32   $76.30   $76.30  
  Purchase #6 $154.73   7.154%   $165.7994   $165.80   $165.80   $165.80  
  Purchase #7 $33.41   11.813%   $37.3567   $37.36   $37.35   $37.40  
  7 purchase totals = $702.21       $763.3898   $763.39   $763.40   $763.40