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 $137.87   10.720%   $152.6497   $152.65   $152.65   $152.60  
  Purchase #2 $226.96   5.160%   $238.6711   $238.67   $238.65   $238.70  
  Purchase #3 $33.76   8.335%   $36.5739   $36.57   $36.55   $36.60  
  Purchase #4 $231.97   6.862%   $247.8878   $247.89   $247.90   $247.90  
  Purchase #5 $59.54   3.208%   $61.45   $61.45   $61.45   $61.50  
  Purchase #6 $203.39   13.373%   $230.5893   $230.59   $230.60   $230.60  
  Purchase #7 $15.37   3.631%   $15.9281   $15.93   $15.95   $15.90  
  7 purchase totals = $908.86       $983.7499   $983.75   $983.75   $983.80