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 $33.51   11.207%   $37.2655   $37.27   $37.25   $37.30  
  Purchase #2 $80.72   8.812%   $87.833   $87.83   $87.85   $87.80  
  Purchase #3 $146.63   5.442%   $154.6096   $154.61   $154.60   $154.60  
  Purchase #4 $214.79   6.187%   $228.0791   $228.08   $228.10   $228.10  
  Purchase #5 $175.79   5.150%   $184.8432   $184.84   $184.85   $184.80  
  Purchase #6 $196.38   11.407%   $218.7811   $218.78   $218.80   $218.80  
  Purchase #7 $101.87   11.175%   $113.254   $113.25   $113.25   $113.30  
  7 purchase totals = $949.69       $1,024.6655   $1,024.66   $1,024.70   $1,024.70