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 $44.81   4.211%   $46.6969   $46.70   $46.70   $46.70  
  Purchase #2 $82.37   11.870%   $92.1473   $92.15   $92.15   $92.10  
  Purchase #3 $103.73   6.459%   $110.4299   $110.43   $110.45   $110.40  
  Purchase #4 $192.31   12.868%   $217.0565   $217.06   $217.05   $217.10  
  Purchase #5 $60.79   6.170%   $64.5407   $64.54   $64.55   $64.50  
  Purchase #6 $6.56   6.331%   $6.9753   $6.98   $7.00   $7.00  
  Purchase #7 $65.77   10.211%   $72.4858   $72.49   $72.50   $72.50  
  7 purchase totals = $556.34       $610.3324   $610.35   $610.40   $610.30