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 $232.69   12.751%   $262.3603   $262.36   $262.35   $262.40  
  Purchase #2 $160.64   4.556%   $167.9588   $167.96   $167.95   $168.00  
  Purchase #3 $84.85   3.813%   $88.0853   $88.09   $88.10   $88.10  
  Purchase #4 $176.71   7.430%   $189.8396   $189.84   $189.85   $189.80  
  Purchase #5 $69.29   13.493%   $78.6393   $78.64   $78.65   $78.60  
  Purchase #6 $38.96   5.840%   $41.2353   $41.24   $41.25   $41.20  
  Purchase #7 $183.39   6.587%   $195.4699   $195.47   $195.45   $195.50  
  7 purchase totals = $946.53       $1,023.5885   $1,023.60   $1,023.60   $1,023.60