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 $157.72   10.748%   $174.6717   $174.67   $174.65   $174.70  
  Purchase #2 $238.90   13.551%   $271.2733   $271.27   $271.25   $271.30  
  Purchase #3 $43.68   11.385%   $48.653   $48.65   $48.65   $48.70  
  Purchase #4 $130.64   6.397%   $138.997   $139.00   $139.00   $139.00  
  Purchase #5 $96.33   5.742%   $101.8613   $101.86   $101.85   $101.90  
  Purchase #6 $221.65   12.848%   $250.1276   $250.13   $250.15   $250.10  
  Purchase #7 $34.69   4.686%   $36.3156   $36.32   $36.30   $36.30  
  7 purchase totals = $923.61       $1,021.8995   $1,021.90   $1,021.85   $1,022.00