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 $61.93   8.620%   $67.2684   $67.27   $67.25   $67.30  
  Purchase #2 $67.65   10.496%   $74.7505   $74.75   $74.75   $74.80  
  Purchase #3 $218.35   3.591%   $226.1909   $226.19   $226.20   $226.20  
  Purchase #4 $12.83   10.393%   $14.1634   $14.16   $14.15   $14.20  
  Purchase #5 $17.34   7.163%   $18.5821   $18.58   $18.60   $18.60  
  Purchase #6 $13.34   3.818%   $13.8493   $13.85   $13.85   $13.80  
  Purchase #7 $24.70   3.292%   $25.5131   $25.51   $25.50   $25.50  
  7 purchase totals = $416.14       $440.3177   $440.31   $440.30   $440.40