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	$75.57	3.413%	$78.1492	$78.15	$78.15	$78.10
Purchase #2	$179.89	10.325%	$198.4636	$198.46	$198.45	$198.50
Purchase #3	$64.40	5.276%	$67.7977	$67.80	$67.80	$67.80
Purchase #4	$170.69	9.488%	$186.8851	$186.89	$186.90	$186.90
Purchase #5	$166.90	3.274%	$172.3643	$172.36	$172.35	$172.40
Purchase #6	$14.42	6.684%	$15.3838	$15.38	$15.40	$15.40
Purchase #7	$51.46	9.799%	$56.5026	$56.50	$56.50	$56.50
7 purchase totals =	$723.33		$775.5463	$775.54	$775.55	$775.60