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 $84.49   13.396%   $95.8083   $95.81   $95.80   $95.80  
  Purchase #2 $14.65   13.383%   $16.6106   $16.61   $16.60   $16.60  
  Purchase #3 $224.57   10.507%   $248.1656   $248.17   $248.15   $248.20  
  Purchase #4 $145.68   6.436%   $155.056   $155.06   $155.05   $155.10  
  Purchase #5 $124.66   10.397%   $137.6209   $137.62   $137.60   $137.60  
  Purchase #6 $54.27   4.616%   $56.7751   $56.78   $56.80   $56.80  
  Purchase #7 $142.25   4.604%   $148.7992   $148.80   $148.80   $148.80  
  7 purchase totals = $790.57       $858.8357   $858.85   $858.80   $858.90