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 $53.80   13.523%   $61.0754   $61.08   $61.10   $61.10  
  Purchase #2 $218.57   13.743%   $248.6081   $248.61   $248.60   $248.60  
  Purchase #3 $184.79   13.357%   $209.4724   $209.47   $209.45   $209.50  
  Purchase #4 $212.48   4.225%   $221.4573   $221.46   $221.45   $221.50  
  Purchase #5 $10.34   4.862%   $10.8427   $10.84   $10.85   $10.80  
  Purchase #6 $180.36   9.627%   $197.7233   $197.72   $197.70   $197.70  
  Purchase #7 $34.29   13.147%   $38.7981   $38.80   $38.80   $38.80  
  7 purchase totals = $894.63       $987.9773   $987.98   $987.95   $988.00