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 $233.63   5.614%   $246.746   $246.75   $246.75   $246.70  
  Purchase #2 $131.99   3.602%   $136.7443   $136.74   $136.75   $136.70  
  Purchase #3 $206.26   5.511%   $217.627   $217.63   $217.65   $217.60  
  Purchase #4 $183.62   4.740%   $192.3236   $192.32   $192.30   $192.30  
  Purchase #5 $7.33   13.273%   $8.3029   $8.30   $8.30   $8.30  
  Purchase #6 $150.72   3.454%   $155.9259   $155.93   $155.95   $155.90  
  Purchase #7 $38.98   11.497%   $43.4615   $43.46   $43.45   $43.50  
  7 purchase totals = $952.53       $1,001.1312   $1,001.13   $1,001.15   $1,001.00