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 $240.34   11.780%   $268.6521   $268.65   $268.65   $268.70  
  Purchase #2 $221.53   12.102%   $248.3396   $248.34   $248.35   $248.30  
  Purchase #3 $61.81   11.272%   $68.7772   $68.78   $68.80   $68.80  
  Purchase #4 $65.79   3.612%   $68.1663   $68.17   $68.15   $68.20  
  Purchase #5 $89.51   4.593%   $93.6212   $93.62   $93.60   $93.60  
  Purchase #6 $13.52   12.865%   $15.2593   $15.26   $15.25   $15.30  
  Purchase #7 $56.67   13.132%   $64.1119   $64.11   $64.10   $64.10  
  7 purchase totals = $749.17       $826.9276   $826.93   $826.90   $827.00