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 $163.42   12.605%   $184.0191   $184.02   $184.00   $184.00  
  Purchase #2 $190.98   7.766%   $205.8115   $205.81   $205.80   $205.80  
  Purchase #3 $26.27   11.218%   $29.217   $29.22   $29.20   $29.20  
  Purchase #4 $207.68   9.566%   $227.5467   $227.55   $227.55   $227.50  
  Purchase #5 $191.30   11.821%   $213.9136   $213.91   $213.90   $213.90  
  Purchase #6 $39.99   7.356%   $42.9317   $42.93   $42.95   $42.90  
  Purchase #7 $27.81   3.755%   $28.8543   $28.85   $28.85   $28.90  
  7 purchase totals = $847.45       $932.2939   $932.29   $932.25   $932.20