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 $51.84   13.364%   $58.7679   $58.77   $58.75   $58.80  
  Purchase #2 $105.83   9.425%   $115.8045   $115.80   $115.80   $115.80  
  Purchase #3 $107.26   4.199%   $111.7638   $111.76   $111.75   $111.80  
  Purchase #4 $57.31   6.251%   $60.8924   $60.89   $60.90   $60.90  
  Purchase #5 $174.52   6.336%   $185.5776   $185.58   $185.60   $185.60  
  Purchase #6 $194.64   11.316%   $216.6655   $216.67   $216.65   $216.70  
  Purchase #7 $183.90   6.119%   $195.1528   $195.15   $195.15   $195.20  
  7 purchase totals = $875.30       $944.6245   $944.62   $944.60   $944.80