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 $81.40   13.805%   $92.6373   $92.64   $92.65   $92.60  
  Purchase #2 $98.56   12.540%   $110.9194   $110.92   $110.90   $110.90  
  Purchase #3 $196.76   6.349%   $209.2523   $209.25   $209.25   $209.30  
  Purchase #4 $241.93   3.243%   $249.7758   $249.78   $249.80   $249.80  
  Purchase #5 $189.78   9.619%   $208.0349   $208.03   $208.05   $208.00  
  Purchase #6 $22.77   3.155%   $23.4884   $23.49   $23.50   $23.50  
  Purchase #7 $113.87   4.215%   $118.6696   $118.67   $118.65   $118.70  
  7 purchase totals = $945.07       $1,012.7777   $1,012.78   $1,012.80   $1,012.80