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 $22.39   11.398%   $24.942   $24.94   $24.95   $24.90  
  Purchase #2 $232.54   3.240%   $240.0743   $240.07   $240.05   $240.10  
  Purchase #3 $122.94   9.851%   $135.0508   $135.05   $135.05   $135.10  
  Purchase #4 $26.96   8.788%   $29.3292   $29.33   $29.35   $29.30  
  Purchase #5 $123.64   11.387%   $137.7189   $137.72   $137.70   $137.70  
  Purchase #6 $242.70   12.385%   $272.7584   $272.76   $272.75   $272.80  
  Purchase #7 $169.44   3.218%   $174.8926   $174.89   $174.90   $174.90  
  7 purchase totals = $940.61       $1,014.7662   $1,014.76   $1,014.75   $1,014.80