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 $22.61   13.520%   $25.6669   $25.67   $25.65   $25.70  
  Purchase #2 $137.71   12.732%   $155.2432   $155.24   $155.25   $155.20  
  Purchase #3 $136.71   6.574%   $145.6973   $145.70   $145.70   $145.70  
  Purchase #4 $156.33   6.801%   $166.962   $166.96   $166.95   $167.00  
  Purchase #5 $172.84   6.787%   $184.5707   $184.57   $184.55   $184.60  
  Purchase #6 $19.70   11.448%   $21.9553   $21.96   $21.95   $22.00  
  Purchase #7 $79.96   6.555%   $85.2014   $85.20   $85.20   $85.20  
  7 purchase totals = $725.86       $785.2968   $785.30   $785.25   $785.40