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 $143.33   7.559%   $154.1643   $154.16   $154.15   $154.20  
  Purchase #2 $192.79   6.504%   $205.3291   $205.33   $205.35   $205.30  
  Purchase #3 $154.89   7.744%   $166.8847   $166.88   $166.90   $166.90  
  Purchase #4 $212.29   8.556%   $230.4535   $230.45   $230.45   $230.50  
  Purchase #5 $131.58   10.493%   $145.3867   $145.39   $145.40   $145.40  
  Purchase #6 $239.69   11.308%   $266.7941   $266.79   $266.80   $266.80  
  Purchase #7 $196.29   8.479%   $212.9334   $212.93   $212.95   $212.90  
  7 purchase totals = $1,270.86       $1,381.9458   $1,381.93   $1,382.00   $1,382.00