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 $221.69   7.297%   $237.8667   $237.87   $237.85   $237.90  
  Purchase #2 $246.63   5.776%   $260.8753   $260.88   $260.90   $260.90  
  Purchase #3 $14.62   5.395%   $15.4087   $15.41   $15.40   $15.40  
  Purchase #4 $132.71   5.769%   $140.366   $140.37   $140.35   $140.40  
  Purchase #5 $134.38   8.339%   $145.5859   $145.59   $145.60   $145.60  
  Purchase #6 $157.72   13.771%   $179.4396   $179.44   $179.45   $179.40  
  Purchase #7 $60.70   6.155%   $64.4361   $64.44   $64.45   $64.40  
  7 purchase totals = $968.45       $1,043.9783   $1,044.00   $1,044.00   $1,044.00