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 $178.51   9.711%   $195.8451   $195.85   $195.85   $195.80  
  Purchase #2 $68.58   3.584%   $71.0379   $71.04   $71.05   $71.00  
  Purchase #3 $160.92   3.634%   $166.7678   $166.77   $166.75   $166.80  
  Purchase #4 $57.54   8.718%   $62.5563   $62.56   $62.55   $62.60  
  Purchase #5 $190.45   6.222%   $202.2998   $202.30   $202.30   $202.30  
  Purchase #6 $62.41   10.628%   $69.0429   $69.04   $69.05   $69.00  
  Purchase #7 $129.57   5.293%   $136.4281   $136.43   $136.45   $136.40  
  7 purchase totals = $847.98       $903.9779   $903.99   $904.00   $903.90