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 $86.78   8.225%   $93.9177   $93.92   $93.90   $93.90  
  Purchase #2 $136.93   11.489%   $152.6619   $152.66   $152.65   $152.70  
  Purchase #3 $195.68   12.571%   $220.2789   $220.28   $220.30   $220.30  
  Purchase #4 $26.75   3.194%   $27.6044   $27.60   $27.60   $27.60  
  Purchase #5 $8.52   11.279%   $9.481   $9.48   $9.50   $9.50  
  Purchase #6 $102.27   11.261%   $113.7866   $113.79   $113.80   $113.80  
  Purchase #7 $55.84   7.289%   $59.9102   $59.91   $59.90   $59.90  
  7 purchase totals = $612.77       $677.6407   $677.64   $677.65   $677.70