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 $107.58   13.406%   $122.0022   $122.00   $122.00   $122.00  
  Purchase #2 $206.49   9.427%   $225.9558   $225.96   $225.95   $226.00  
  Purchase #3 $92.71   6.429%   $98.6703   $98.67   $98.65   $98.70  
  Purchase #4 $77.84   12.577%   $87.6299   $87.63   $87.65   $87.60  
  Purchase #5 $70.36   6.777%   $75.1283   $75.13   $75.15   $75.10  
  Purchase #6 $162.53   7.725%   $175.0854   $175.09   $175.10   $175.10  
  Purchase #7 $162.29   5.560%   $171.3133   $171.31   $171.30   $171.30  
  7 purchase totals = $879.80       $955.7852   $955.79   $955.80   $955.80