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 $195.35   11.107%   $217.0475   $217.05   $217.05   $217.00  
  Purchase #2 $34.84   9.826%   $38.2634   $38.26   $38.25   $38.30  
  Purchase #3 $202.25   6.256%   $214.9028   $214.90   $214.90   $214.90  
  Purchase #4 $58.42   9.593%   $64.0242   $64.02   $64.00   $64.00  
  Purchase #5 $224.39   8.658%   $243.8177   $243.82   $243.80   $243.80  
  Purchase #6 $5.38   7.305%   $5.773   $5.77   $5.75   $5.80  
  Purchase #7 $71.46   11.447%   $79.64   $79.64   $79.65   $79.60  
  7 purchase totals = $792.09       $863.4686   $863.46   $863.40   $863.40