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 $184.69   11.838%   $206.5536   $206.55   $206.55   $206.60  
  Purchase #2 $61.59   10.787%   $68.2337   $68.23   $68.25   $68.20  
  Purchase #3 $104.32   10.578%   $115.355   $115.36   $115.35   $115.40  
  Purchase #4 $88.77   9.720%   $97.3984   $97.40   $97.40   $97.40  
  Purchase #5 $179.73   8.410%   $194.8453   $194.85   $194.85   $194.80  
  Purchase #6 $70.90   8.717%   $77.0804   $77.08   $77.10   $77.10  
  Purchase #7 $124.28   9.767%   $136.4184   $136.42   $136.40   $136.40  
  7 purchase totals = $814.28       $895.8848   $895.89   $895.90   $895.90