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 $60.54   8.273%   $65.5485   $65.55   $65.55   $65.50  
  Purchase #2 $145.47   4.571%   $152.1194   $152.12   $152.10   $152.10  
  Purchase #3 $97.46   3.782%   $101.1459   $101.15   $101.15   $101.10  
  Purchase #4 $237.70   6.452%   $253.0364   $253.04   $253.05   $253.00  
  Purchase #5 $247.38   11.356%   $275.4725   $275.47   $275.45   $275.50  
  Purchase #6 $220.29   13.222%   $249.4167   $249.42   $249.40   $249.40  
  Purchase #7 $165.52   7.359%   $177.7006   $177.70   $177.70   $177.70  
  7 purchase totals = $1,174.36       $1,274.4400   $1,274.45   $1,274.40   $1,274.30