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 $236.61   12.398%   $265.9449   $265.94   $265.95   $265.90  
  Purchase #2 $63.99   7.197%   $68.5954   $68.60   $68.60   $68.60  
  Purchase #3 $232.90   13.730%   $264.8772   $264.88   $264.90   $264.90  
  Purchase #4 $164.88   8.613%   $179.0811   $179.08   $179.10   $179.10  
  Purchase #5 $28.37   11.630%   $31.6694   $31.67   $31.65   $31.70  
  Purchase #6 $148.75   5.617%   $157.1053   $157.11   $157.10   $157.10  
  Purchase #7 $61.48   9.836%   $67.5272   $67.53   $67.55   $67.50  
  7 purchase totals = $936.98       $1,034.8005   $1,034.81   $1,034.85   $1,034.80