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 $174.25   12.219%   $195.5416   $195.54   $195.55   $195.50  
  Purchase #2 $62.92   5.830%   $66.5882   $66.59   $66.60   $66.60  
  Purchase #3 $58.53   8.596%   $63.5612   $63.56   $63.55   $63.60  
  Purchase #4 $201.28   12.371%   $226.1803   $226.18   $226.20   $226.20  
  Purchase #5 $243.90   13.495%   $276.8143   $276.81   $276.80   $276.80  
  Purchase #6 $51.35   9.559%   $56.2585   $56.26   $56.25   $56.30  
  Purchase #7 $95.42   8.718%   $103.7387   $103.74   $103.75   $103.70  
  7 purchase totals = $887.65       $988.6828   $988.68   $988.70   $988.70