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 $89.61   3.265%   $92.5358   $92.54   $92.55   $92.50  
  Purchase #2 $206.68   9.492%   $226.2981   $226.30   $226.30   $226.30  
  Purchase #3 $171.92   3.497%   $177.932   $177.93   $177.95   $177.90  
  Purchase #4 $164.72   10.112%   $181.3765   $181.38   $181.40   $181.40  
  Purchase #5 $10.28   13.509%   $11.6687   $11.67   $11.65   $11.70  
  Purchase #6 $219.92   10.847%   $243.7747   $243.77   $243.75   $243.80  
  Purchase #7 $59.76   10.480%   $66.0228   $66.02   $66.00   $66.00  
  7 purchase totals = $922.89       $999.6086   $999.61   $999.60   $999.60