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 $220.74   7.830%   $238.0239   $238.02   $238.00   $238.00  
  Purchase #2 $200.51   8.384%   $217.3208   $217.32   $217.30   $217.30  
  Purchase #3 $38.95   5.478%   $41.0837   $41.08   $41.10   $41.10  
  Purchase #4 $245.66   6.859%   $262.5098   $262.51   $262.50   $262.50  
  Purchase #5 $141.91   13.590%   $161.1956   $161.20   $161.20   $161.20  
  Purchase #6 $118.31   5.670%   $125.0182   $125.02   $125.00   $125.00  
  Purchase #7 $205.29   8.293%   $222.3147   $222.31   $222.30   $222.30  
  7 purchase totals = $1,171.37       $1,267.4667   $1,267.46   $1,267.40   $1,267.40