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 $73.67   11.838%   $82.3911   $82.39   $82.40   $82.40  
  Purchase #2 $220.35   12.213%   $247.2613   $247.26   $247.25   $247.30  
  Purchase #3 $97.33   10.761%   $107.8037   $107.80   $107.80   $107.80  
  Purchase #4 $233.62   11.621%   $260.769   $260.77   $260.75   $260.80  
  Purchase #5 $56.88   5.661%   $60.1   $60.10   $60.10   $60.10  
  Purchase #6 $170.25   6.755%   $181.7504   $181.75   $181.75   $181.80  
  Purchase #7 $50.64   7.548%   $54.4623   $54.46   $54.45   $54.50  
  7 purchase totals = $902.74       $994.5378   $994.53   $994.50   $994.70