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 $167.59   8.273%   $181.4547   $181.45   $181.45   $181.50  
  Purchase #2 $62.57   9.301%   $68.3896   $68.39   $68.40   $68.40  
  Purchase #3 $164.75   8.261%   $178.36   $178.36   $178.35   $178.40  
  Purchase #4 $241.37   4.291%   $251.7272   $251.73   $251.75   $251.70  
  Purchase #5 $184.35   11.316%   $205.211   $205.21   $205.20   $205.20  
  Purchase #6 $176.76   6.506%   $188.26   $188.26   $188.25   $188.30  
  Purchase #7 $233.96   8.465%   $253.7647   $253.76   $253.75   $253.80  
  7 purchase totals = $1,231.35       $1,327.1672   $1,327.16   $1,327.15   $1,327.30