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 $59.78   10.258%   $65.9122   $65.91   $65.90   $65.90  
  Purchase #2 $224.75   13.140%   $254.2822   $254.28   $254.30   $254.30  
  Purchase #3 $106.47   8.850%   $115.8926   $115.89   $115.90   $115.90  
  Purchase #4 $105.88   10.803%   $117.3182   $117.32   $117.30   $117.30  
  Purchase #5 $127.66   3.840%   $132.5621   $132.56   $132.55   $132.60  
  Purchase #6 $216.38   12.590%   $243.6222   $243.62   $243.60   $243.60  
  Purchase #7 $34.55   6.600%   $36.8303   $36.83   $36.85   $36.80  
  7 purchase totals = $875.47       $966.4198   $966.41   $966.40   $966.40