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 $216.78   7.686%   $233.4417   $233.44   $233.45   $233.40  
  Purchase #2 $155.96   12.179%   $174.9544   $174.95   $174.95   $175.00  
  Purchase #3 $234.29   3.194%   $241.7732   $241.77   $241.75   $241.80  
  Purchase #4 $249.42   3.809%   $258.9204   $258.92   $258.90   $258.90  
  Purchase #5 $183.67   12.127%   $205.9437   $205.94   $205.95   $205.90  
  Purchase #6 $134.26   7.814%   $144.7511   $144.75   $144.75   $144.80  
  Purchase #7 $35.36   7.305%   $37.943   $37.94   $37.95   $37.90  
  7 purchase totals = $1,209.74       $1,297.7275   $1,297.71   $1,297.70   $1,297.70