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 $40.73   13.362%   $46.1723   $46.17   $46.15   $46.20  
  Purchase #2 $173.43   6.208%   $184.1965   $184.20   $184.20   $184.20  
  Purchase #3 $226.59   9.345%   $247.7648   $247.76   $247.75   $247.80  
  Purchase #4 $215.48   8.710%   $234.2483   $234.25   $234.25   $234.20  
  Purchase #5 $245.87   12.247%   $275.9817   $275.98   $276.00   $276.00  
  Purchase #6 $175.37   7.777%   $189.0085   $189.01   $189.00   $189.00  
  Purchase #7 $147.83   13.118%   $167.2223   $167.22   $167.20   $167.20  
  7 purchase totals = $1,225.30       $1,344.5944   $1,344.59   $1,344.55   $1,344.60