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 $242.94   9.472%   $265.9513   $265.95   $265.95   $266.00  
  Purchase #2 $37.75   3.764%   $39.1709   $39.17   $39.15   $39.20  
  Purchase #3 $247.58   9.829%   $271.9146   $271.91   $271.90   $271.90  
  Purchase #4 $50.86   5.250%   $53.5302   $53.53   $53.55   $53.50  
  Purchase #5 $122.83   13.263%   $139.1209   $139.12   $139.10   $139.10  
  Purchase #6 $219.96   12.805%   $248.1259   $248.13   $248.15   $248.10  
  Purchase #7 $21.50   12.448%   $24.1763   $24.18   $24.20   $24.20  
  7 purchase totals = $943.42       $1,041.9901   $1,041.99   $1,042.00   $1,042.00