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 $92.79   3.480%   $96.0191   $96.02   $96.00   $96.00  
  Purchase #2 $6.33   8.348%   $6.8584   $6.86   $6.85   $6.90  
  Purchase #3 $43.78   5.731%   $46.289   $46.29   $46.30   $46.30  
  Purchase #4 $249.97   4.844%   $262.0785   $262.08   $262.10   $262.10  
  Purchase #5 $120.88   13.240%   $136.8845   $136.88   $136.90   $136.90  
  Purchase #6 $241.93   8.280%   $261.9618   $261.96   $261.95   $262.00  
  Purchase #7 $184.35   6.421%   $196.1871   $196.19   $196.20   $196.20  
  7 purchase totals = $940.03       $1,006.2784   $1,006.28   $1,006.30   $1,006.40