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 $224.91   7.432%   $241.6253   $241.63   $241.65   $241.60  
  Purchase #2 $46.65   6.652%   $49.7532   $49.75   $49.75   $49.80  
  Purchase #3 $25.72   13.503%   $29.193   $29.19   $29.20   $29.20  
  Purchase #4 $67.48   6.815%   $72.0788   $72.08   $72.10   $72.10  
  Purchase #5 $75.67   11.436%   $84.3236   $84.32   $84.30   $84.30  
  Purchase #6 $56.42   12.665%   $63.5656   $63.57   $63.55   $63.60  
  Purchase #7 $242.99   4.458%   $253.8225   $253.82   $253.80   $253.80  
  7 purchase totals = $739.84       $794.3620   $794.36   $794.35   $794.40