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 $209.46   13.304%   $237.3266   $237.33   $237.35   $237.30  
  Purchase #2 $61.47   6.634%   $65.5479   $65.55   $65.55   $65.50  
  Purchase #3 $183.65   3.216%   $189.5562   $189.56   $189.55   $189.60  
  Purchase #4 $153.67   13.182%   $173.9268   $173.93   $173.95   $173.90  
  Purchase #5 $182.81   6.347%   $194.413   $194.41   $194.40   $194.40  
  Purchase #6 $240.75   6.123%   $255.4911   $255.49   $255.50   $255.50  
  Purchase #7 $172.32   6.311%   $183.1951   $183.20   $183.20   $183.20  
  7 purchase totals = $1,204.13       $1,299.4567   $1,299.47   $1,299.50   $1,299.40