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 $171.68   8.637%   $186.508   $186.51   $186.50   $186.50  
  Purchase #2 $85.86   13.475%   $97.4296   $97.43   $97.45   $97.40  
  Purchase #3 $208.65   9.869%   $229.2417   $229.24   $229.25   $229.20  
  Purchase #4 $74.96   5.773%   $79.2874   $79.29   $79.30   $79.30  
  Purchase #5 $201.33   7.612%   $216.6552   $216.66   $216.65   $216.70  
  Purchase #6 $108.91   12.839%   $122.893   $122.89   $122.90   $122.90  
  Purchase #7 $113.89   12.515%   $128.1433   $128.14   $128.15   $128.10  
  7 purchase totals = $965.28       $1,060.1582   $1,060.16   $1,060.20   $1,060.10