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 $204.46   11.147%   $227.2512   $227.25   $227.25   $227.30  
  Purchase #2 $28.25   7.621%   $30.4029   $30.40   $30.40   $30.40  
  Purchase #3 $139.89   3.373%   $144.6085   $144.61   $144.60   $144.60  
  Purchase #4 $178.96   6.575%   $190.7266   $190.73   $190.75   $190.70  
  Purchase #5 $185.48   9.189%   $202.5238   $202.52   $202.50   $202.50  
  Purchase #6 $159.60   13.190%   $180.6512   $180.65   $180.65   $180.70  
  Purchase #7 $65.69   13.713%   $74.6981   $74.70   $74.70   $74.70  
  7 purchase totals = $962.33       $1,050.8623   $1,050.86   $1,050.85   $1,050.90