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 $170.49   7.774%   $183.7439   $183.74   $183.75   $183.70  
  Purchase #2 $230.98   5.138%   $242.8478   $242.85   $242.85   $242.80  
  Purchase #3 $108.49   10.318%   $119.684   $119.68   $119.70   $119.70  
  Purchase #4 $97.61   4.781%   $102.2767   $102.28   $102.30   $102.30  
  Purchase #5 $192.33   10.715%   $212.9382   $212.94   $212.95   $212.90  
  Purchase #6 $55.75   3.486%   $57.6934   $57.69   $57.70   $57.70  
  Purchase #7 $99.75   3.349%   $103.0906   $103.09   $103.10   $103.10  
  7 purchase totals = $955.40       $1,022.2746   $1,022.27   $1,022.35   $1,022.20