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 $125.37   13.131%   $141.8323   $141.83   $141.85   $141.80  
  Purchase #2 $41.92   4.597%   $43.8471   $43.85   $43.85   $43.80  
  Purchase #3 $11.28   10.383%   $12.4512   $12.45   $12.45   $12.50  
  Purchase #4 $195.70   4.628%   $204.757   $204.76   $204.75   $204.80  
  Purchase #5 $171.29   13.800%   $194.928   $194.93   $194.95   $194.90  
  Purchase #6 $63.77   12.221%   $71.5633   $71.56   $71.55   $71.60  
  Purchase #7 $246.41   8.581%   $267.5544   $267.55   $267.55   $267.60  
  7 purchase totals = $855.74       $936.9333   $936.93   $936.95   $937.00