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 $164.78   8.489%   $178.7682   $178.77   $178.75   $178.80  
  Purchase #2 $127.93   7.523%   $137.5542   $137.55   $137.55   $137.60  
  Purchase #3 $195.37   4.820%   $204.7868   $204.79   $204.80   $204.80  
  Purchase #4 $112.92   5.522%   $119.1554   $119.16   $119.15   $119.20  
  Purchase #5 $87.59   3.751%   $90.8755   $90.88   $90.90   $90.90  
  Purchase #6 $155.84   5.599%   $164.5655   $164.57   $164.55   $164.60  
  Purchase #7 $146.66   7.515%   $157.6815   $157.68   $157.70   $157.70  
  7 purchase totals = $991.09       $1,053.3871   $1,053.40   $1,053.40   $1,053.60