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 $248.38   6.166%   $263.6951   $263.70   $263.70   $263.70  
  Purchase #2 $8.47   8.480%   $9.1883   $9.19   $9.20   $9.20  
  Purchase #3 $124.74   5.492%   $131.5907   $131.59   $131.60   $131.60  
  Purchase #4 $217.25   3.704%   $225.2969   $225.30   $225.30   $225.30  
  Purchase #5 $127.83   4.814%   $133.9837   $133.98   $134.00   $134.00  
  Purchase #6 $155.73   11.272%   $173.2839   $173.28   $173.30   $173.30  
  Purchase #7 $70.74   4.471%   $73.9028   $73.90   $73.90   $73.90  
  7 purchase totals = $953.14       $1,010.9414   $1,010.94   $1,011.00   $1,011.00