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 $245.37   11.267%   $273.0158   $273.02   $273.00   $273.00  
  Purchase #2 $244.65   4.175%   $254.8641   $254.86   $254.85   $254.90  
  Purchase #3 $206.67   13.712%   $235.0086   $235.01   $235.00   $235.00  
  Purchase #4 $217.30   11.470%   $242.2243   $242.22   $242.20   $242.20  
  Purchase #5 $170.26   9.216%   $185.9512   $185.95   $185.95   $186.00  
  Purchase #6 $22.52   6.490%   $23.9815   $23.98   $24.00   $24.00  
  Purchase #7 $140.75   4.239%   $146.7164   $146.72   $146.70   $146.70  
  7 purchase totals = $1,247.52       $1,361.7619   $1,361.76   $1,361.70   $1,361.80