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 $230.84   5.596%   $243.7578   $243.76   $243.75   $243.80  
  Purchase #2 $13.68   12.234%   $15.3536   $15.35   $15.35   $15.40  
  Purchase #3 $68.91   12.294%   $77.3818   $77.38   $77.40   $77.40  
  Purchase #4 $200.95   6.815%   $214.6447   $214.64   $214.65   $214.60  
  Purchase #5 $103.53   5.820%   $109.5554   $109.56   $109.55   $109.60  
  Purchase #6 $62.51   11.802%   $69.8874   $69.89   $69.90   $69.90  
  Purchase #7 $17.47   11.576%   $19.4923   $19.49   $19.50   $19.50  
  7 purchase totals = $697.89       $750.0730   $750.07   $750.10   $750.20