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 $56.41   8.859%   $61.4074   $61.41   $61.40   $61.40  
  Purchase #2 $94.53   7.464%   $101.5857   $101.59   $101.60   $101.60  
  Purchase #3 $191.26   7.272%   $205.1684   $205.17   $205.15   $205.20  
  Purchase #4 $161.66   3.869%   $167.9146   $167.91   $167.90   $167.90  
  Purchase #5 $132.91   6.417%   $141.4388   $141.44   $141.45   $141.40  
  Purchase #6 $65.45   6.556%   $69.7409   $69.74   $69.75   $69.70  
  Purchase #7 $229.81   10.168%   $253.1771   $253.18   $253.20   $253.20  
  7 purchase totals = $932.03       $1,000.4329   $1,000.44   $1,000.45   $1,000.40