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 $49.70   12.535%   $55.9299   $55.93   $55.95   $55.90  
  Purchase #2 $177.82   6.202%   $188.8484   $188.85   $188.85   $188.80  
  Purchase #3 $23.61   11.348%   $26.2893   $26.29   $26.30   $26.30  
  Purchase #4 $188.39   9.626%   $206.5244   $206.52   $206.50   $206.50  
  Purchase #5 $12.87   9.238%   $14.0589   $14.06   $14.05   $14.10  
  Purchase #6 $187.37   9.351%   $204.891   $204.89   $204.90   $204.90  
  Purchase #7 $186.52   13.629%   $211.9408   $211.94   $211.95   $211.90  
  7 purchase totals = $826.28       $908.4827   $908.48   $908.50   $908.40