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 $56.73   9.643%   $62.2005   $62.20   $62.20   $62.20  
  Purchase #2 $16.52   4.411%   $17.2487   $17.25   $17.25   $17.20  
  Purchase #3 $107.59   5.453%   $113.4569   $113.46   $113.45   $113.50  
  Purchase #4 $227.90   10.142%   $251.0136   $251.01   $251.00   $251.00  
  Purchase #5 $197.52   9.387%   $216.0612   $216.06   $216.05   $216.10  
  Purchase #6 $46.92   7.493%   $50.4357   $50.44   $50.45   $50.40  
  Purchase #7 $171.70   8.529%   $186.3443   $186.34   $186.35   $186.30  
  7 purchase totals = $824.88       $896.7609   $896.76   $896.75   $896.70