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 $217.86   6.516%   $232.0558   $232.06   $232.05   $232.10  
  Purchase #2 $185.43   4.284%   $193.3738   $193.37   $193.35   $193.40  
  Purchase #3 $133.69   7.465%   $143.67   $143.67   $143.65   $143.70  
  Purchase #4 $65.52   4.486%   $68.4592   $68.46   $68.45   $68.50  
  Purchase #5 $125.55   7.271%   $134.6787   $134.68   $134.70   $134.70  
  Purchase #6 $227.28   5.511%   $239.8054   $239.81   $239.80   $239.80  
  Purchase #7 $172.52   9.280%   $188.5299   $188.53   $188.55   $188.50  
  7 purchase totals = $1,127.85       $1,200.5728   $1,200.58   $1,200.55   $1,200.70