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 $237.57   11.775%   $265.5439   $265.54   $265.55   $265.50  
  Purchase #2 $108.81   9.863%   $119.5419   $119.54   $119.55   $119.50  
  Purchase #3 $14.49   12.714%   $16.3323   $16.33   $16.35   $16.30  
  Purchase #4 $227.27   6.215%   $241.3948   $241.39   $241.40   $241.40  
  Purchase #5 $138.86   9.722%   $152.36   $152.36   $152.35   $152.40  
  Purchase #6 $99.26   4.549%   $103.7753   $103.78   $103.80   $103.80  
  Purchase #7 $165.81   10.250%   $182.8055   $182.81   $182.80   $182.80  
  7 purchase totals = $992.07       $1,081.7537   $1,081.75   $1,081.80   $1,081.70