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 $10.77   3.134%   $11.1075   $11.11   $11.10   $11.10  
  Purchase #2 $179.71   7.737%   $193.6142   $193.61   $193.60   $193.60  
  Purchase #3 $110.89   5.490%   $116.9779   $116.98   $117.00   $117.00  
  Purchase #4 $134.55   7.645%   $144.8363   $144.84   $144.85   $144.80  
  Purchase #5 $47.47   11.429%   $52.8953   $52.90   $52.90   $52.90  
  Purchase #6 $67.93   4.420%   $70.9325   $70.93   $70.95   $70.90  
  Purchase #7 $62.72   7.720%   $67.562   $67.56   $67.55   $67.60  
  7 purchase totals = $614.04       $657.9257   $657.93   $657.95   $657.90