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 $244.53   11.534%   $272.7341   $272.73   $272.75   $272.70  
  Purchase #2 $147.25   9.495%   $161.2314   $161.23   $161.25   $161.20  
  Purchase #3 $114.64   11.559%   $127.8912   $127.89   $127.90   $127.90  
  Purchase #4 $22.30   7.348%   $23.9386   $23.94   $23.95   $23.90  
  Purchase #5 $77.60   5.515%   $81.8796   $81.88   $81.90   $81.90  
  Purchase #6 $211.81   3.783%   $219.8228   $219.82   $219.80   $219.80  
  Purchase #7 $40.53   8.571%   $44.0038   $44.00   $44.00   $44.00  
  7 purchase totals = $858.66       $931.5015   $931.49   $931.55   $931.40