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 $57.96   5.855%   $61.3536   $61.35   $61.35   $61.40  
  Purchase #2 $249.92   7.595%   $268.9014   $268.90   $268.90   $268.90  
  Purchase #3 $165.99   5.723%   $175.4896   $175.49   $175.50   $175.50  
  Purchase #4 $15.90   7.445%   $17.0838   $17.08   $17.10   $17.10  
  Purchase #5 $175.78   9.233%   $192.0098   $192.01   $192.00   $192.00  
  Purchase #6 $54.36   12.440%   $61.1224   $61.12   $61.10   $61.10  
  Purchase #7 $24.96   3.857%   $25.9227   $25.92   $25.90   $25.90  
  7 purchase totals = $744.87       $801.8833   $801.87   $801.85   $801.90