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 $56.45   12.558%   $63.539   $63.54   $63.55   $63.50  
  Purchase #2 $21.29   9.514%   $23.3155   $23.32   $23.30   $23.30  
  Purchase #3 $240.32   6.631%   $256.2556   $256.26   $256.25   $256.30  
  Purchase #4 $203.93   8.706%   $221.6841   $221.68   $221.70   $221.70  
  Purchase #5 $218.57   8.280%   $236.6676   $236.67   $236.65   $236.70  
  Purchase #6 $187.57   6.714%   $200.1634   $200.16   $200.15   $200.20  
  Purchase #7 $30.50   8.804%   $33.1852   $33.19   $33.20   $33.20  
  7 purchase totals = $958.63       $1,034.8104   $1,034.82   $1,034.80   $1,034.90