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 $58.97   5.592%   $62.2676   $62.27   $62.25   $62.30  
  Purchase #2 $183.43   8.171%   $198.4181   $198.42   $198.40   $198.40  
  Purchase #3 $98.95   12.584%   $111.4019   $111.40   $111.40   $111.40  
  Purchase #4 $157.59   11.787%   $176.1651   $176.17   $176.15   $176.20  
  Purchase #5 $159.46   7.387%   $171.2393   $171.24   $171.25   $171.20  
  Purchase #6 $183.30   10.568%   $202.6711   $202.67   $202.65   $202.70  
  Purchase #7 $43.99   9.701%   $48.2575   $48.26   $48.25   $48.30  
  7 purchase totals = $885.69       $970.4206   $970.43   $970.35   $970.50