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 $92.51   4.306%   $96.4935   $96.49   $96.50   $96.50  
  Purchase #2 $102.40   5.314%   $107.8415   $107.84   $107.85   $107.80  
  Purchase #3 $150.30   5.608%   $158.7288   $158.73   $158.75   $158.70  
  Purchase #4 $177.46   6.688%   $189.3285   $189.33   $189.35   $189.30  
  Purchase #5 $53.76   5.807%   $56.8818   $56.88   $56.90   $56.90  
  Purchase #6 $161.99   7.325%   $173.8558   $173.86   $173.85   $173.90  
  Purchase #7 $157.30   6.230%   $167.0998   $167.10   $167.10   $167.10  
  7 purchase totals = $895.72       $950.2297   $950.23   $950.30   $950.20