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 $55.73   4.654%   $58.3237   $58.32   $58.30   $58.30  
  Purchase #2 $246.76   12.244%   $276.9733   $276.97   $276.95   $277.00  
  Purchase #3 $18.58   11.211%   $20.663   $20.66   $20.65   $20.70  
  Purchase #4 $79.32   8.753%   $86.2629   $86.26   $86.25   $86.30  
  Purchase #5 $129.47   6.247%   $137.558   $137.56   $137.55   $137.60  
  Purchase #6 $186.85   7.429%   $200.7311   $200.73   $200.75   $200.70  
  Purchase #7 $91.35   13.774%   $103.9325   $103.93   $103.95   $103.90  
  7 purchase totals = $808.06       $884.4445   $884.43   $884.40   $884.50