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 $116.76   13.106%   $132.0626   $132.06   $132.05   $132.10  
  Purchase #2 $79.84   10.405%   $88.1474   $88.15   $88.15   $88.10  
  Purchase #3 $92.80   11.581%   $103.5472   $103.55   $103.55   $103.50  
  Purchase #4 $68.44   3.651%   $70.9387   $70.94   $70.95   $70.90  
  Purchase #5 $165.56   12.575%   $186.3792   $186.38   $186.40   $186.40  
  Purchase #6 $244.81   3.846%   $254.2254   $254.23   $254.25   $254.20  
  Purchase #7 $156.43   8.412%   $169.5889   $169.59   $169.60   $169.60  
  7 purchase totals = $924.64       $1,004.8894   $1,004.90   $1,004.95   $1,004.80