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 $47.27   13.658%   $53.7261   $53.73   $53.75   $53.70  
  Purchase #2 $169.37   10.663%   $187.4299   $187.43   $187.45   $187.40  
  Purchase #3 $107.59   5.163%   $113.1449   $113.14   $113.15   $113.10  
  Purchase #4 $148.99   9.166%   $162.6464   $162.65   $162.65   $162.60  
  Purchase #5 $12.47   11.666%   $13.9248   $13.92   $13.90   $13.90  
  Purchase #6 $41.86   10.160%   $46.113   $46.11   $46.10   $46.10  
  Purchase #7 $181.45   11.361%   $202.0645   $202.06   $202.05   $202.10  
  7 purchase totals = $709.00       $779.0496   $779.04   $779.05   $778.90