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 $67.51   12.448%   $75.9136   $75.91   $75.90   $75.90  
  Purchase #2 $141.85   13.254%   $160.6508   $160.65   $160.65   $160.70  
  Purchase #3 $199.52   9.338%   $218.1512   $218.15   $218.15   $218.20  
  Purchase #4 $60.51   13.718%   $68.8108   $68.81   $68.80   $68.80  
  Purchase #5 $219.82   10.105%   $242.0328   $242.03   $242.05   $242.00  
  Purchase #6 $56.43   3.804%   $58.5766   $58.58   $58.60   $58.60  
  Purchase #7 $5.88   12.711%   $6.6274   $6.63   $6.65   $6.60  
  7 purchase totals = $751.52       $830.7632   $830.76   $830.80   $830.80