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 $24.47   7.394%   $26.2793   $26.28   $26.30   $26.30  
  Purchase #2 $72.93   3.336%   $75.3629   $75.36   $75.35   $75.40  
  Purchase #3 $24.72   9.477%   $27.0627   $27.06   $27.05   $27.10  
  Purchase #4 $20.67   9.103%   $22.5516   $22.55   $22.55   $22.60  
  Purchase #5 $79.68   7.249%   $85.456   $85.46   $85.45   $85.50  
  Purchase #6 $244.52   11.657%   $273.0237   $273.02   $273.00   $273.00  
  Purchase #7 $54.62   8.724%   $59.385   $59.39   $59.40   $59.40  
  7 purchase totals = $521.61       $569.1212   $569.12   $569.10   $569.30