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 $246.25   6.372%   $261.9411   $261.94   $261.95   $261.90  
  Purchase #2 $107.62   12.838%   $121.4363   $121.44   $121.45   $121.40  
  Purchase #3 $5.74   10.458%   $6.3403   $6.34   $6.35   $6.30  
  Purchase #4 $25.95   11.219%   $28.8613   $28.86   $28.85   $28.90  
  Purchase #5 $167.35   3.835%   $173.7679   $173.77   $173.75   $173.80  
  Purchase #6 $104.56   13.631%   $118.8126   $118.81   $118.80   $118.80  
  Purchase #7 $153.77   11.760%   $171.8534   $171.85   $171.85   $171.90  
  7 purchase totals = $811.24       $883.0129   $883.01   $883.00   $883.00