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 $60.85   12.766%   $68.6181   $68.62   $68.60   $68.60  
  Purchase #2 $98.36   11.388%   $109.5612   $109.56   $109.55   $109.60  
  Purchase #3 $248.97   11.831%   $278.4256   $278.43   $278.45   $278.40  
  Purchase #4 $65.44   7.204%   $70.1543   $70.15   $70.15   $70.20  
  Purchase #5 $176.33   8.134%   $190.6727   $190.67   $190.65   $190.70  
  Purchase #6 $116.97   5.511%   $123.4162   $123.42   $123.40   $123.40  
  Purchase #7 $186.91   9.159%   $204.0291   $204.03   $204.05   $204.00  
  7 purchase totals = $953.83       $1,044.8772   $1,044.88   $1,044.85   $1,044.90