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 $84.58   10.651%   $93.5886   $93.59   $93.60   $93.60  
  Purchase #2 $199.88   11.397%   $222.6603   $222.66   $222.65   $222.70  
  Purchase #3 $97.39   4.847%   $102.1105   $102.11   $102.10   $102.10  
  Purchase #4 $98.35   10.600%   $108.7751   $108.78   $108.80   $108.80  
  Purchase #5 $169.57   9.486%   $185.6554   $185.66   $185.65   $185.70  
  Purchase #6 $8.29   11.379%   $9.2333   $9.23   $9.25   $9.20  
  Purchase #7 $14.41   8.332%   $15.6106   $15.61   $15.60   $15.60  
  7 purchase totals = $672.47       $737.6338   $737.64   $737.65   $737.70