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 $244.64   6.173%   $259.7416   $259.74   $259.75   $259.70  
  Purchase #2 $67.95   12.210%   $76.2467   $76.25   $76.25   $76.20  
  Purchase #3 $51.32   4.700%   $53.732   $53.73   $53.75   $53.70  
  Purchase #4 $182.76   11.694%   $204.132   $204.13   $204.15   $204.10  
  Purchase #5 $182.57   13.646%   $207.4835   $207.48   $207.50   $207.50  
  Purchase #6 $21.27   4.597%   $22.2478   $22.25   $22.25   $22.20  
  Purchase #7 $189.77   11.636%   $211.8516   $211.85   $211.85   $211.90  
  7 purchase totals = $940.28       $1,035.4352   $1,035.43   $1,035.50   $1,035.30