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 $190.47   7.781%   $205.2905   $205.29   $205.30   $205.30  
  Purchase #2 $228.62   4.734%   $239.4429   $239.44   $239.45   $239.40  
  Purchase #3 $114.58   5.206%   $120.545   $120.55   $120.55   $120.50  
  Purchase #4 $95.74   7.361%   $102.7874   $102.79   $102.80   $102.80  
  Purchase #5 $69.56   6.655%   $74.1892   $74.19   $74.20   $74.20  
  Purchase #6 $33.49   12.526%   $37.685   $37.69   $37.70   $37.70  
  Purchase #7 $235.99   4.811%   $247.3435   $247.34   $247.35   $247.30  
  7 purchase totals = $968.45       $1,027.2835   $1,027.29   $1,027.35   $1,027.20