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 $134.56   5.226%   $141.5921   $141.59   $141.60   $141.60  
  Purchase #2 $154.79   13.698%   $175.9931   $175.99   $176.00   $176.00  
  Purchase #3 $83.73   12.184%   $93.9317   $93.93   $93.95   $93.90  
  Purchase #4 $235.64   5.760%   $249.2129   $249.21   $249.20   $249.20  
  Purchase #5 $82.36   11.172%   $91.5613   $91.56   $91.55   $91.60  
  Purchase #6 $24.74   10.209%   $27.2657   $27.27   $27.25   $27.30  
  Purchase #7 $230.97   6.110%   $245.0823   $245.08   $245.10   $245.10  
  7 purchase totals = $946.79       $1,024.6391   $1,024.63   $1,024.65   $1,024.70