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 $53.86   12.833%   $60.7719   $60.77   $60.75   $60.80  
  Purchase #2 $91.41   5.184%   $96.1487   $96.15   $96.15   $96.10  
  Purchase #3 $228.78   6.182%   $242.9232   $242.92   $242.90   $242.90  
  Purchase #4 $222.65   12.200%   $249.8133   $249.81   $249.80   $249.80  
  Purchase #5 $49.80   7.401%   $53.4857   $53.49   $53.50   $53.50  
  Purchase #6 $129.43   3.804%   $134.3535   $134.35   $134.35   $134.40  
  Purchase #7 $204.58   11.563%   $228.2356   $228.24   $228.25   $228.20  
  7 purchase totals = $980.51       $1,065.7319   $1,065.73   $1,065.70   $1,065.70