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 $56.50   11.352%   $62.9139   $62.91   $62.90   $62.90  
  Purchase #2 $189.36   4.226%   $197.3624   $197.36   $197.35   $197.40  
  Purchase #3 $184.32   12.231%   $206.8642   $206.86   $206.85   $206.90  
  Purchase #4 $217.48   3.521%   $225.1375   $225.14   $225.15   $225.10  
  Purchase #5 $67.29   4.119%   $70.0617   $70.06   $70.05   $70.10  
  Purchase #6 $220.34   3.697%   $228.486   $228.49   $228.50   $228.50  
  Purchase #7 $7.79   8.502%   $8.4523   $8.45   $8.45   $8.50  
  7 purchase totals = $943.08       $999.2780   $999.27   $999.25   $999.40