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 $65.31   5.622%   $68.9817   $68.98   $69.00   $69.00  
  Purchase #2 $23.46   6.241%   $24.9241   $24.92   $24.90   $24.90  
  Purchase #3 $193.94   12.855%   $218.871   $218.87   $218.85   $218.90  
  Purchase #4 $81.50   12.605%   $91.7731   $91.77   $91.75   $91.80  
  Purchase #5 $209.95   5.199%   $220.8653   $220.87   $220.85   $220.90  
  Purchase #6 $154.85   10.292%   $170.7872   $170.79   $170.80   $170.80  
  Purchase #7 $206.89   5.267%   $217.7869   $217.79   $217.80   $217.80  
  7 purchase totals = $935.90       $1,013.9893   $1,013.99   $1,013.95   $1,014.10