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 $70.86   7.221%   $75.9768   $75.98   $76.00   $76.00  
  Purchase #2 $116.95   3.183%   $120.6725   $120.67   $120.65   $120.70  
  Purchase #3 $6.88   10.853%   $7.6267   $7.63   $7.65   $7.60  
  Purchase #4 $205.44   7.682%   $221.2219   $221.22   $221.20   $221.20  
  Purchase #5 $177.76   10.186%   $195.8666   $195.87   $195.85   $195.90  
  Purchase #6 $237.51   13.463%   $269.486   $269.49   $269.50   $269.50  
  Purchase #7 $25.38   9.801%   $27.8675   $27.87   $27.85   $27.90  
  7 purchase totals = $840.78       $918.7180   $918.73   $918.70   $918.80