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 $226.74   10.108%   $249.6589   $249.66   $249.65   $249.70  
  Purchase #2 $88.32   7.366%   $94.8257   $94.83   $94.85   $94.80  
  Purchase #3 $22.56   8.341%   $24.4417   $24.44   $24.45   $24.40  
  Purchase #4 $244.77   9.725%   $268.5739   $268.57   $268.55   $268.60  
  Purchase #5 $179.74   3.746%   $186.4731   $186.47   $186.45   $186.50  
  Purchase #6 $16.72   5.259%   $17.5993   $17.60   $17.60   $17.60  
  Purchase #7 $187.54   4.484%   $195.9493   $195.95   $195.95   $195.90  
  7 purchase totals = $966.39       $1,037.5219   $1,037.52   $1,037.50   $1,037.50