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 $75.79   8.232%   $82.029   $82.03   $82.05   $82.00  
  Purchase #2 $48.72   4.326%   $50.8276   $50.83   $50.85   $50.80  
  Purchase #3 $173.85   8.825%   $189.1923   $189.19   $189.20   $189.20  
  Purchase #4 $248.78   7.732%   $268.0157   $268.02   $268.00   $268.00  
  Purchase #5 $166.90   5.589%   $176.228   $176.23   $176.25   $176.20  
  Purchase #6 $24.72   7.258%   $26.5142   $26.51   $26.50   $26.50  
  Purchase #7 $17.49   4.535%   $18.2832   $18.28   $18.30   $18.30  
  7 purchase totals = $756.25       $811.0900   $811.09   $811.15   $811.00