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 $235.58   13.609%   $267.6401   $267.64   $267.65   $267.60  
  Purchase #2 $215.97   12.207%   $242.3335   $242.33   $242.35   $242.30  
  Purchase #3 $208.64   8.118%   $225.5774   $225.58   $225.60   $225.60  
  Purchase #4 $20.81   5.670%   $21.9899   $21.99   $22.00   $22.00  
  Purchase #5 $229.42   4.479%   $239.6957   $239.70   $239.70   $239.70  
  Purchase #6 $31.99   4.266%   $33.3547   $33.35   $33.35   $33.40  
  Purchase #7 $223.58   10.264%   $246.5283   $246.53   $246.55   $246.50  
  7 purchase totals = $1,165.99       $1,277.1196   $1,277.12   $1,277.20   $1,277.10