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 $211.43   13.317%   $239.5861   $239.59   $239.60   $239.60  
  Purchase #2 $124.29   8.830%   $135.2648   $135.26   $135.25   $135.30  
  Purchase #3 $98.51   11.262%   $109.6042   $109.60   $109.60   $109.60  
  Purchase #4 $151.43   3.336%   $156.4817   $156.48   $156.50   $156.50  
  Purchase #5 $137.97   11.576%   $153.9414   $153.94   $153.95   $153.90  
  Purchase #6 $131.53   13.371%   $149.1169   $149.12   $149.10   $149.10  
  Purchase #7 $96.59   11.400%   $107.6013   $107.60   $107.60   $107.60  
  7 purchase totals = $951.75       $1,051.5964   $1,051.59   $1,051.60   $1,051.60