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 $53.29   6.871%   $56.9516   $56.95   $56.95   $57.00  
  Purchase #2 $247.32   8.766%   $269.0001   $269.00   $269.00   $269.00  
  Purchase #3 $103.69   8.252%   $112.2465   $112.25   $112.25   $112.20  
  Purchase #4 $106.36   3.755%   $110.3538   $110.35   $110.35   $110.40  
  Purchase #5 $166.63   12.254%   $187.0488   $187.05   $187.05   $187.00  
  Purchase #6 $245.37   13.499%   $278.4925   $278.49   $278.50   $278.50  
  Purchase #7 $240.71   5.281%   $253.4219   $253.42   $253.40   $253.40  
  7 purchase totals = $1,163.37       $1,267.5152   $1,267.51   $1,267.50   $1,267.50