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 $219.61   12.414%   $246.8724   $246.87   $246.85   $246.90  
  Purchase #2 $96.74   4.682%   $101.2694   $101.27   $101.25   $101.30  
  Purchase #3 $168.26   9.782%   $184.7192   $184.72   $184.70   $184.70  
  Purchase #4 $64.92   4.671%   $67.9524   $67.95   $67.95   $68.00  
  Purchase #5 $168.41   3.300%   $173.9675   $173.97   $173.95   $174.00  
  Purchase #6 $241.28   5.291%   $254.0461   $254.05   $254.05   $254.00  
  Purchase #7 $249.26   13.831%   $283.7352   $283.74   $283.75   $283.70  
  7 purchase totals = $1,208.48       $1,312.5622   $1,312.57   $1,312.50   $1,312.60