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 $178.89   8.600%   $194.2745   $194.27   $194.25   $194.30  
  Purchase #2 $227.94   7.399%   $244.8053   $244.81   $244.80   $244.80  
  Purchase #3 $156.47   3.871%   $162.527   $162.53   $162.55   $162.50  
  Purchase #4 $115.95   8.215%   $125.4753   $125.48   $125.50   $125.50  
  Purchase #5 $186.55   8.849%   $203.0578   $203.06   $203.05   $203.10  
  Purchase #6 $85.66   10.496%   $94.6509   $94.65   $94.65   $94.70  
  Purchase #7 $184.77   13.813%   $210.2923   $210.29   $210.30   $210.30  
  7 purchase totals = $1,136.23       $1,235.0831   $1,235.09   $1,235.10   $1,235.20