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 $246.78   6.611%   $263.0946   $263.09   $263.10   $263.10  
  Purchase #2 $98.95   12.481%   $111.2999   $111.30   $111.30   $111.30  
  Purchase #3 $243.36   9.110%   $265.5301   $265.53   $265.55   $265.50  
  Purchase #4 $23.64   7.540%   $25.4225   $25.42   $25.40   $25.40  
  Purchase #5 $198.71   4.623%   $207.8964   $207.90   $207.90   $207.90  
  Purchase #6 $170.49   9.768%   $187.1435   $187.14   $187.15   $187.10  
  Purchase #7 $162.94   5.460%   $171.8365   $171.84   $171.85   $171.80  
  7 purchase totals = $1,144.87       $1,232.2235   $1,232.22   $1,232.25   $1,232.10