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 $31.46   13.567%   $35.7282   $35.73   $35.75   $35.70  
  Purchase #2 $240.88   4.730%   $252.2736   $252.27   $252.25   $252.30  
  Purchase #3 $242.53   3.736%   $251.5909   $251.59   $251.60   $251.60  
  Purchase #4 $39.29   11.706%   $43.8893   $43.89   $43.90   $43.90  
  Purchase #5 $124.76   9.673%   $136.828   $136.83   $136.85   $136.80  
  Purchase #6 $209.36   11.640%   $233.7295   $233.73   $233.75   $233.70  
  Purchase #7 $179.71   11.364%   $200.1322   $200.13   $200.15   $200.10  
  7 purchase totals = $1,067.99       $1,154.1717   $1,154.17   $1,154.25   $1,154.10