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 $117.97   10.159%   $129.9546   $129.95   $129.95   $130.00  
  Purchase #2 $208.99   8.544%   $226.8461   $226.85   $226.85   $226.80  
  Purchase #3 $243.76   7.286%   $261.5204   $261.52   $261.50   $261.50  
  Purchase #4 $36.57   8.339%   $39.6196   $39.62   $39.60   $39.60  
  Purchase #5 $242.40   12.168%   $271.8952   $271.90   $271.90   $271.90  
  Purchase #6 $44.71   13.172%   $50.5992   $50.60   $50.60   $50.60  
  Purchase #7 $203.46   8.833%   $221.4316   $221.43   $221.45   $221.40  
  7 purchase totals = $1,097.86       $1,201.8667   $1,201.87   $1,201.85   $1,201.80