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 $84.52   9.187%   $92.2849   $92.28   $92.30   $92.30  
  Purchase #2 $51.26   4.488%   $53.5605   $53.56   $53.55   $53.60  
  Purchase #3 $245.32   10.132%   $270.1758   $270.18   $270.20   $270.20  
  Purchase #4 $207.67   4.146%   $216.28   $216.28   $216.30   $216.30  
  Purchase #5 $153.74   9.544%   $168.4129   $168.41   $168.40   $168.40  
  Purchase #6 $190.68   12.205%   $213.9525   $213.95   $213.95   $214.00  
  Purchase #7 $20.53   4.348%   $21.4226   $21.42   $21.40   $21.40  
  7 purchase totals = $953.72       $1,036.0892   $1,036.08   $1,036.10   $1,036.20