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 $215.70   12.103%   $241.8062   $241.81   $241.80   $241.80  
  Purchase #2 $178.67   6.612%   $190.4837   $190.48   $190.50   $190.50  
  Purchase #3 $168.98   8.869%   $183.9668   $183.97   $183.95   $184.00  
  Purchase #4 $142.60   4.209%   $148.602   $148.60   $148.60   $148.60  
  Purchase #5 $175.80   6.568%   $187.3465   $187.35   $187.35   $187.30  
  Purchase #6 $241.27   6.325%   $256.5303   $256.53   $256.55   $256.50  
  Purchase #7 $90.67   6.352%   $96.4294   $96.43   $96.45   $96.40  
  7 purchase totals = $1,213.69       $1,305.1649   $1,305.17   $1,305.20   $1,305.10