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 $147.93   12.394%   $166.2644   $166.26   $166.25   $166.30  
  Purchase #2 $68.43   10.104%   $75.3442   $75.34   $75.35   $75.30  
  Purchase #3 $117.40   5.246%   $123.5588   $123.56   $123.55   $123.60  
  Purchase #4 $182.81   3.294%   $188.8318   $188.83   $188.85   $188.80  
  Purchase #5 $180.49   12.492%   $203.0368   $203.04   $203.05   $203.00  
  Purchase #6 $248.93   6.666%   $265.5237   $265.52   $265.50   $265.50  
  Purchase #7 $232.40   3.290%   $240.046   $240.05   $240.05   $240.00  
  7 purchase totals = $1,178.39       $1,262.6057   $1,262.60   $1,262.60   $1,262.50