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 $151.44   11.779%   $169.2781   $169.28   $169.30   $169.30  
  Purchase #2 $45.47   4.168%   $47.3652   $47.37   $47.35   $47.40  
  Purchase #3 $118.96   8.170%   $128.679   $128.68   $128.70   $128.70  
  Purchase #4 $241.31   12.594%   $271.7006   $271.70   $271.70   $271.70  
  Purchase #5 $64.99   13.272%   $73.6155   $73.62   $73.60   $73.60  
  Purchase #6 $94.99   11.393%   $105.8122   $105.81   $105.80   $105.80  
  Purchase #7 $202.35   7.344%   $217.2106   $217.21   $217.20   $217.20  
  7 purchase totals = $919.51       $1,013.6612   $1,013.67   $1,013.65   $1,013.70