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 $106.58   11.464%   $118.7983   $118.80   $118.80   $118.80  
  Purchase #2 $223.25   10.398%   $246.4635   $246.46   $246.45   $246.50  
  Purchase #3 $241.64   5.270%   $254.3744   $254.37   $254.35   $254.40  
  Purchase #4 $115.41   10.679%   $127.7346   $127.73   $127.75   $127.70  
  Purchase #5 $66.88   5.506%   $70.5624   $70.56   $70.55   $70.60  
  Purchase #6 $68.80   9.381%   $75.2541   $75.25   $75.25   $75.30  
  Purchase #7 $244.84   7.284%   $262.6741   $262.67   $262.65   $262.70  
  7 purchase totals = $1,067.40       $1,155.8614   $1,155.84   $1,155.80   $1,156.00