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 $235.54   10.776%   $260.9218   $260.92   $260.90   $260.90  
  Purchase #2 $185.55   10.393%   $204.8342   $204.83   $204.85   $204.80  
  Purchase #3 $222.83   7.499%   $239.54   $239.54   $239.55   $239.50  
  Purchase #4 $217.36   8.123%   $235.0162   $235.02   $235.00   $235.00  
  Purchase #5 $172.79   9.402%   $189.0357   $189.04   $189.05   $189.00  
  Purchase #6 $243.64   3.412%   $251.953   $251.95   $251.95   $252.00  
  Purchase #7 $141.30   3.209%   $145.8343   $145.83   $145.85   $145.80  
  7 purchase totals = $1,419.01       $1,527.1352   $1,527.13   $1,527.15   $1,527.00