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 $245.63   11.576%   $274.0641   $274.06   $274.05   $274.10  
  Purchase #2 $68.78   3.613%   $71.265   $71.27   $71.25   $71.30  
  Purchase #3 $16.53   4.111%   $17.2095   $17.21   $17.20   $17.20  
  Purchase #4 $22.27   7.222%   $23.8783   $23.88   $23.90   $23.90  
  Purchase #5 $98.84   3.744%   $102.5406   $102.54   $102.55   $102.50  
  Purchase #6 $165.79   5.382%   $174.7128   $174.71   $174.70   $174.70  
  Purchase #7 $216.70   6.432%   $230.6381   $230.64   $230.65   $230.60  
  7 purchase totals = $834.54       $894.3084   $894.31   $894.30   $894.30