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 $57.65   11.514%   $64.2878   $64.29   $64.30   $64.30  
  Purchase #2 $204.68   5.132%   $215.1842   $215.18   $215.20   $215.20  
  Purchase #3 $53.37   5.871%   $56.5034   $56.50   $56.50   $56.50  
  Purchase #4 $159.61   10.438%   $176.2701   $176.27   $176.25   $176.30  
  Purchase #5 $222.76   8.463%   $241.6122   $241.61   $241.60   $241.60  
  Purchase #6 $183.57   10.439%   $202.7329   $202.73   $202.75   $202.70  
  Purchase #7 $196.30   3.344%   $202.8643   $202.86   $202.85   $202.90  
  7 purchase totals = $1,077.94       $1,159.4549   $1,159.44   $1,159.45   $1,159.50