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 $176.47   11.411%   $196.607   $196.61   $196.60   $196.60  
  Purchase #2 $11.26   13.285%   $12.7559   $12.76   $12.75   $12.80  
  Purchase #3 $25.46   6.231%   $27.0464   $27.05   $27.05   $27.00  
  Purchase #4 $160.86   10.377%   $177.5524   $177.55   $177.55   $177.60  
  Purchase #5 $247.52   4.711%   $259.1807   $259.18   $259.20   $259.20  
  Purchase #6 $139.32   8.202%   $150.747   $150.75   $150.75   $150.70  
  Purchase #7 $190.50   3.825%   $197.7866   $197.79   $197.80   $197.80  
  7 purchase totals = $951.39       $1,021.6760   $1,021.69   $1,021.70   $1,021.70