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 $85.71   8.867%   $93.3099   $93.31   $93.30   $93.30  
  Purchase #2 $171.47   11.153%   $190.594   $190.59   $190.60   $190.60  
  Purchase #3 $5.39   12.602%   $6.0692   $6.07   $6.05   $6.10  
  Purchase #4 $54.40   12.593%   $61.2506   $61.25   $61.25   $61.30  
  Purchase #5 $213.35   3.145%   $220.0599   $220.06   $220.05   $220.10  
  Purchase #6 $182.79   12.749%   $206.0939   $206.09   $206.10   $206.10  
  Purchase #7 $86.32   10.720%   $95.5735   $95.57   $95.55   $95.60  
  7 purchase totals = $799.43       $872.9510   $872.94   $872.90   $873.10