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 $212.36   10.580%   $234.8277   $234.83   $234.85   $234.80  
  Purchase #2 $86.75   12.445%   $97.546   $97.55   $97.55   $97.50  
  Purchase #3 $156.39   8.513%   $169.7035   $169.70   $169.70   $169.70  
  Purchase #4 $241.86   6.541%   $257.6801   $257.68   $257.70   $257.70  
  Purchase #5 $66.84   3.848%   $69.412   $69.41   $69.40   $69.40  
  Purchase #6 $202.48   7.382%   $217.4271   $217.43   $217.45   $217.40  
  Purchase #7 $93.96   4.189%   $97.896   $97.90   $97.90   $97.90  
  7 purchase totals = $1,060.64       $1,144.4924   $1,144.50   $1,144.55   $1,144.40