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 $85.53   13.352%   $96.95   $96.95   $96.95   $97.00  
  Purchase #2 $51.48   13.403%   $58.3799   $58.38   $58.40   $58.40  
  Purchase #3 $81.75   4.685%   $85.58   $85.58   $85.60   $85.60  
  Purchase #4 $235.88   7.792%   $254.2598   $254.26   $254.25   $254.30  
  Purchase #5 $102.68   3.295%   $106.0633   $106.06   $106.05   $106.10  
  Purchase #6 $112.41   9.107%   $122.6472   $122.65   $122.65   $122.60  
  Purchase #7 $73.68   10.386%   $81.3324   $81.33   $81.35   $81.30  
  7 purchase totals = $743.41       $805.2126   $805.21   $805.25   $805.30