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 $46.68   5.569%   $49.2796   $49.28   $49.30   $49.30  
  Purchase #2 $128.97   3.564%   $133.5665   $133.57   $133.55   $133.60  
  Purchase #3 $15.29   3.347%   $15.8018   $15.80   $15.80   $15.80  
  Purchase #4 $158.64   5.689%   $167.665   $167.67   $167.65   $167.70  
  Purchase #5 $130.42   6.141%   $138.4291   $138.43   $138.45   $138.40  
  Purchase #6 $126.55   6.385%   $134.6302   $134.63   $134.65   $134.60  
  Purchase #7 $125.51   9.102%   $136.9339   $136.93   $136.95   $136.90  
  7 purchase totals = $732.06       $776.3061   $776.31   $776.35   $776.30