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 $205.82   8.667%   $223.6584   $223.66   $223.65   $223.70  
  Purchase #2 $237.58   12.147%   $266.4388   $266.44   $266.45   $266.40  
  Purchase #3 $84.45   3.737%   $87.6059   $87.61   $87.60   $87.60  
  Purchase #4 $139.83   11.479%   $155.8811   $155.88   $155.90   $155.90  
  Purchase #5 $88.47   7.667%   $95.253   $95.25   $95.25   $95.30  
  Purchase #6 $137.95   11.157%   $153.3411   $153.34   $153.35   $153.30  
  Purchase #7 $149.94   4.352%   $156.4654   $156.47   $156.45   $156.50  
  7 purchase totals = $1,044.04       $1,138.6437   $1,138.65   $1,138.65   $1,138.70