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 $248.65   11.520%   $277.2945   $277.29   $277.30   $277.30  
  Purchase #2 $29.68   11.271%   $33.0252   $33.03   $33.05   $33.00  
  Purchase #3 $139.77   12.841%   $157.7179   $157.72   $157.70   $157.70  
  Purchase #4 $183.64   5.381%   $193.5217   $193.52   $193.50   $193.50  
  Purchase #5 $184.42   11.113%   $204.9146   $204.91   $204.90   $204.90  
  Purchase #6 $71.52   4.735%   $74.9065   $74.91   $74.90   $74.90  
  Purchase #7 $10.83   11.766%   $12.1043   $12.10   $12.10   $12.10  
  7 purchase totals = $868.51       $953.4847   $953.48   $953.45   $953.40