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 $85.75   7.768%   $92.4111   $92.41   $92.40   $92.40  
  Purchase #2 $108.95   11.811%   $121.8181   $121.82   $121.80   $121.80  
  Purchase #3 $129.84   8.797%   $141.262   $141.26   $141.25   $141.30  
  Purchase #4 $244.42   8.135%   $264.3036   $264.30   $264.30   $264.30  
  Purchase #5 $98.65   5.407%   $103.984   $103.98   $104.00   $104.00  
  Purchase #6 $113.25   13.698%   $128.763   $128.76   $128.75   $128.80  
  Purchase #7 $58.83   10.263%   $64.8677   $64.87   $64.85   $64.90  
  7 purchase totals = $839.69       $917.4095   $917.40   $917.35   $917.50