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 $16.86   3.235%   $17.4054   $17.41   $17.40   $17.40  
  Purchase #2 $126.35   13.139%   $142.9511   $142.95   $142.95   $143.00  
  Purchase #3 $107.61   12.297%   $120.8428   $120.84   $120.85   $120.80  
  Purchase #4 $205.78   7.157%   $220.5077   $220.51   $220.50   $220.50  
  Purchase #5 $175.48   13.298%   $198.8153   $198.82   $198.80   $198.80  
  Purchase #6 $90.66   4.651%   $94.8766   $94.88   $94.90   $94.90  
  Purchase #7 $67.73   3.318%   $69.9773   $69.98   $70.00   $70.00  
  7 purchase totals = $790.47       $865.3762   $865.39   $865.40   $865.40