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 $34.63   9.585%   $37.9493   $37.95   $37.95   $37.90  
  Purchase #2 $150.46   7.404%   $161.6001   $161.60   $161.60   $161.60  
  Purchase #3 $177.28   5.622%   $187.2467   $187.25   $187.25   $187.20  
  Purchase #4 $69.35   6.278%   $73.7038   $73.70   $73.70   $73.70  
  Purchase #5 $96.37   8.771%   $104.8226   $104.82   $104.80   $104.80  
  Purchase #6 $75.81   9.847%   $83.275   $83.28   $83.30   $83.30  
  Purchase #7 $182.43   8.276%   $197.5279   $197.53   $197.55   $197.50  
  7 purchase totals = $786.33       $846.1254   $846.13   $846.15   $846.00