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 $184.34   3.228%   $190.2905   $190.29   $190.30   $190.30  
  Purchase #2 $86.84   10.508%   $95.9651   $95.97   $95.95   $96.00  
  Purchase #3 $218.44   4.337%   $227.9137   $227.91   $227.90   $227.90  
  Purchase #4 $204.54   4.669%   $214.09   $214.09   $214.10   $214.10  
  Purchase #5 $60.63   10.279%   $66.8622   $66.86   $66.85   $66.90  
  Purchase #6 $46.28   6.823%   $49.4377   $49.44   $49.45   $49.40  
  Purchase #7 $23.64   3.724%   $24.5204   $24.52   $24.50   $24.50  
  7 purchase totals = $824.71       $869.0796   $869.08   $869.05   $869.10