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 $88.92   8.291%   $96.2924   $96.29   $96.30   $96.30  
  Purchase #2 $250.31   6.168%   $265.7491   $265.75   $265.75   $265.70  
  Purchase #3 $15.44   5.568%   $16.2997   $16.30   $16.30   $16.30  
  Purchase #4 $29.64   5.226%   $31.189   $31.19   $31.20   $31.20  
  Purchase #5 $110.90   8.572%   $120.4063   $120.41   $120.40   $120.40  
  Purchase #6 $133.91   10.824%   $148.4044   $148.40   $148.40   $148.40  
  Purchase #7 $87.74   3.560%   $90.8635   $90.86   $90.85   $90.90  
  7 purchase totals = $716.86       $769.2044   $769.20   $769.20   $769.20