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 $151.64   6.705%   $161.8075   $161.81   $161.80   $161.80  
  Purchase #2 $187.46   3.825%   $194.6303   $194.63   $194.65   $194.60  
  Purchase #3 $119.62   11.174%   $132.9863   $132.99   $133.00   $133.00  
  Purchase #4 $140.94   11.788%   $157.554   $157.55   $157.55   $157.60  
  Purchase #5 $157.38   6.673%   $167.882   $167.88   $167.90   $167.90  
  Purchase #6 $65.79   13.507%   $74.6763   $74.68   $74.70   $74.70  
  Purchase #7 $107.40   11.470%   $119.7188   $119.72   $119.70   $119.70  
  7 purchase totals = $930.23       $1,009.2552   $1,009.26   $1,009.30   $1,009.30