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 $162.54   13.756%   $184.899   $184.90   $184.90   $184.90  
  Purchase #2 $223.87   11.829%   $250.3516   $250.35   $250.35   $250.40  
  Purchase #3 $150.77   12.527%   $169.657   $169.66   $169.65   $169.70  
  Purchase #4 $139.89   13.568%   $158.8703   $158.87   $158.85   $158.90  
  Purchase #5 $238.58   3.662%   $247.3168   $247.32   $247.30   $247.30  
  Purchase #6 $64.66   9.564%   $70.8441   $70.84   $70.85   $70.80  
  Purchase #7 $174.95   5.271%   $184.1716   $184.17   $184.15   $184.20  
  7 purchase totals = $1,155.26       $1,266.1104   $1,266.11   $1,266.05   $1,266.20