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 $245.58   6.276%   $260.9926   $260.99   $261.00   $261.00  
  Purchase #2 $130.76   3.831%   $135.7694   $135.77   $135.75   $135.80  
  Purchase #3 $109.38   5.225%   $115.0951   $115.10   $115.10   $115.10  
  Purchase #4 $238.87   3.759%   $247.8491   $247.85   $247.85   $247.80  
  Purchase #5 $191.54   11.873%   $214.2815   $214.28   $214.30   $214.30  
  Purchase #6 $38.59   13.150%   $43.6646   $43.66   $43.65   $43.70  
  Purchase #7 $71.32   5.510%   $75.2497   $75.25   $75.25   $75.20  
  7 purchase totals = $1,026.04       $1,092.9020   $1,092.90   $1,092.90   $1,092.90