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 $113.93   7.703%   $122.706   $122.71   $122.70   $122.70  
  Purchase #2 $128.86   8.550%   $139.8775   $139.88   $139.90   $139.90  
  Purchase #3 $139.99   12.298%   $157.206   $157.21   $157.20   $157.20  
  Purchase #4 $87.41   11.567%   $97.5207   $97.52   $97.50   $97.50  
  Purchase #5 $208.47   6.457%   $221.9309   $221.93   $221.95   $221.90  
  Purchase #6 $181.66   10.421%   $200.5908   $200.59   $200.60   $200.60  
  Purchase #7 $79.78   5.363%   $84.0586   $84.06   $84.05   $84.10  
  7 purchase totals = $940.10       $1,023.8905   $1,023.90   $1,023.90   $1,023.90