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 $235.59   4.718%   $246.7051   $246.71   $246.70   $246.70  
  Purchase #2 $12.36   5.747%   $13.0703   $13.07   $13.05   $13.10  
  Purchase #3 $45.84   3.684%   $47.5287   $47.53   $47.55   $47.50  
  Purchase #4 $229.67   4.685%   $240.43   $240.43   $240.45   $240.40  
  Purchase #5 $232.77   8.697%   $253.014   $253.01   $253.00   $253.00  
  Purchase #6 $147.47   11.864%   $164.9658   $164.97   $164.95   $165.00  
  Purchase #7 $95.93   8.388%   $103.9766   $103.98   $104.00   $104.00  
  7 purchase totals = $999.63       $1,069.6905   $1,069.70   $1,069.70   $1,069.70