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 $69.53   5.277%   $73.1991   $73.20   $73.20   $73.20  
  Purchase #2 $125.90   13.548%   $142.9569   $142.96   $142.95   $143.00  
  Purchase #3 $195.80   5.539%   $206.6454   $206.65   $206.65   $206.60  
  Purchase #4 $215.53   11.322%   $239.9323   $239.93   $239.95   $239.90  
  Purchase #5 $72.72   11.774%   $81.2821   $81.28   $81.30   $81.30  
  Purchase #6 $67.47   11.869%   $75.478   $75.48   $75.50   $75.50  
  Purchase #7 $235.50   10.237%   $259.6081   $259.61   $259.60   $259.60  
  7 purchase totals = $982.45       $1,079.1019   $1,079.11   $1,079.15   $1,079.10