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 $36.90   6.243%   $39.2037   $39.20   $39.20   $39.20  
  Purchase #2 $228.36   12.135%   $256.0715   $256.07   $256.05   $256.10  
  Purchase #3 $162.75   3.459%   $168.3795   $168.38   $168.40   $168.40  
  Purchase #4 $157.91   4.488%   $164.997   $165.00   $165.00   $165.00  
  Purchase #5 $130.34   4.250%   $135.8795   $135.88   $135.90   $135.90  
  Purchase #6 $25.84   4.222%   $26.931   $26.93   $26.95   $26.90  
  Purchase #7 $209.43   11.240%   $232.9699   $232.97   $232.95   $233.00  
  7 purchase totals = $951.53       $1,024.4321   $1,024.43   $1,024.45   $1,024.50