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 $129.35   3.816%   $134.286   $134.29   $134.30   $134.30  
  Purchase #2 $22.92   7.737%   $24.6933   $24.69   $24.70   $24.70  
  Purchase #3 $192.42   8.445%   $208.6699   $208.67   $208.65   $208.70  
  Purchase #4 $233.52   5.546%   $246.471   $246.47   $246.45   $246.50  
  Purchase #5 $32.30   4.377%   $33.7138   $33.71   $33.70   $33.70  
  Purchase #6 $171.79   9.369%   $187.885   $187.89   $187.90   $187.90  
  Purchase #7 $173.95   7.819%   $187.5512   $187.55   $187.55   $187.60  
  7 purchase totals = $956.25       $1,023.2702   $1,023.27   $1,023.25   $1,023.40