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 $135.87   11.798%   $151.8999   $151.90   $151.90   $151.90  
  Purchase #2 $200.25   4.185%   $208.6305   $208.63   $208.65   $208.60  
  Purchase #3 $102.39   10.662%   $113.3068   $113.31   $113.30   $113.30  
  Purchase #4 $195.55   8.807%   $212.7721   $212.77   $212.75   $212.80  
  Purchase #5 $223.59   9.224%   $244.2139   $244.21   $244.20   $244.20  
  Purchase #6 $182.43   11.593%   $203.5791   $203.58   $203.60   $203.60  
  Purchase #7 $104.44   6.103%   $110.814   $110.81   $110.80   $110.80  
  7 purchase totals = $1,144.52       $1,245.2163   $1,245.21   $1,245.20   $1,245.20