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 $183.73   13.126%   $207.8464   $207.85   $207.85   $207.80  
  Purchase #2 $93.81   4.111%   $97.6665   $97.67   $97.65   $97.70  
  Purchase #3 $169.51   10.455%   $187.2323   $187.23   $187.25   $187.20  
  Purchase #4 $100.77   11.813%   $112.674   $112.67   $112.65   $112.70  
  Purchase #5 $170.48   8.154%   $184.3809   $184.38   $184.40   $184.40  
  Purchase #6 $154.46   12.736%   $174.132   $174.13   $174.15   $174.10  
  Purchase #7 $135.41   10.444%   $149.5522   $149.55   $149.55   $149.60  
  7 purchase totals = $1,008.17       $1,113.4843   $1,113.48   $1,113.50   $1,113.50