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 $147.97   12.627%   $166.6542   $166.65   $166.65   $166.70  
  Purchase #2 $211.28   5.536%   $222.9765   $222.98   $223.00   $223.00  
  Purchase #3 $170.94   10.346%   $188.6255   $188.63   $188.65   $188.60  
  Purchase #4 $241.62   13.311%   $273.782   $273.78   $273.80   $273.80  
  Purchase #5 $9.62   10.802%   $10.6592   $10.66   $10.65   $10.70  
  Purchase #6 $68.41   11.256%   $76.1102   $76.11   $76.10   $76.10  
  Purchase #7 $235.73   5.520%   $248.7423   $248.74   $248.75   $248.70  
  7 purchase totals = $1,085.57       $1,187.5499   $1,187.55   $1,187.60   $1,187.60