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 $54.29   11.110%   $60.3216   $60.32   $60.30   $60.30  
  Purchase #2 $244.71   5.394%   $257.9097   $257.91   $257.90   $257.90  
  Purchase #3 $21.81   7.704%   $23.4902   $23.49   $23.50   $23.50  
  Purchase #4 $87.63   3.677%   $90.8522   $90.85   $90.85   $90.90  
  Purchase #5 $208.70   5.170%   $219.4898   $219.49   $219.50   $219.50  
  Purchase #6 $170.36   6.622%   $181.6412   $181.64   $181.65   $181.60  
  Purchase #7 $64.96   13.412%   $73.6724   $73.67   $73.65   $73.70  
  7 purchase totals = $852.46       $907.3771   $907.37   $907.35   $907.40