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 $246.55   10.529%   $272.5092   $272.51   $272.50   $272.50  
  Purchase #2 $127.62   5.662%   $134.8458   $134.85   $134.85   $134.80  
  Purchase #3 $192.39   4.106%   $200.2895   $200.29   $200.30   $200.30  
  Purchase #4 $101.92   7.556%   $109.6211   $109.62   $109.60   $109.60  
  Purchase #5 $192.64   5.339%   $202.925   $202.93   $202.95   $202.90  
  Purchase #6 $162.59   3.683%   $168.5782   $168.58   $168.60   $168.60  
  Purchase #7 $249.73   3.159%   $257.619   $257.62   $257.60   $257.60  
  7 purchase totals = $1,273.44       $1,346.3878   $1,346.40   $1,346.40   $1,346.30