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 $143.70   5.112%   $151.0459   $151.05   $151.05   $151.00  
  Purchase #2 $56.32   9.277%   $61.5448   $61.54   $61.55   $61.50  
  Purchase #3 $250.87   8.769%   $272.8688   $272.87   $272.85   $272.90  
  Purchase #4 $54.99   10.515%   $60.7722   $60.77   $60.75   $60.80  
  Purchase #5 $230.32   9.529%   $252.2672   $252.27   $252.25   $252.30  
  Purchase #6 $240.25   5.234%   $252.8247   $252.82   $252.80   $252.80  
  Purchase #7 $146.25   3.619%   $151.5428   $151.54   $151.55   $151.50  
  7 purchase totals = $1,122.70       $1,202.8664   $1,202.86   $1,202.80   $1,202.80