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 $58.80   3.794%   $61.0309   $61.03   $61.05   $61.00  
  Purchase #2 $28.53   3.146%   $29.4276   $29.43   $29.45   $29.40  
  Purchase #3 $223.84   3.844%   $232.4444   $232.44   $232.45   $232.40  
  Purchase #4 $159.61   4.484%   $166.7669   $166.77   $166.75   $166.80  
  Purchase #5 $191.90   9.297%   $209.7409   $209.74   $209.75   $209.70  
  Purchase #6 $200.56   3.723%   $208.0268   $208.03   $208.05   $208.00  
  Purchase #7 $131.71   5.710%   $139.2306   $139.23   $139.25   $139.20  
  7 purchase totals = $994.95       $1,046.6681   $1,046.67   $1,046.75   $1,046.50