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 $65.83   5.184%   $69.2426   $69.24   $69.25   $69.20  
  Purchase #2 $246.42   7.711%   $265.4214   $265.42   $265.40   $265.40  
  Purchase #3 $212.61   5.186%   $223.636   $223.64   $223.65   $223.60  
  Purchase #4 $131.90   4.560%   $137.9146   $137.91   $137.90   $137.90  
  Purchase #5 $249.47   12.773%   $281.3348   $281.33   $281.35   $281.30  
  Purchase #6 $38.51   8.659%   $41.8446   $41.84   $41.85   $41.80  
  Purchase #7 $14.43   8.592%   $15.6698   $15.67   $15.65   $15.70  
  7 purchase totals = $959.17       $1,035.0638   $1,035.05   $1,035.05   $1,034.90