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	$159.37	12.614%	$179.4729	$179.47	$179.45	$179.50
Purchase #2	$98.29	9.383%	$107.5126	$107.51	$107.50	$107.50
Purchase #3	$245.76	11.241%	$273.3859	$273.39	$273.40	$273.40
Purchase #4	$196.33	9.602%	$215.1816	$215.18	$215.20	$215.20
Purchase #5	$39.78	13.467%	$45.1372	$45.14	$45.15	$45.10
Purchase #6	$96.54	7.666%	$103.9408	$103.94	$103.95	$103.90
Purchase #7	$89.70	7.409%	$96.3459	$96.35	$96.35	$96.30
7 purchase totals =	$925.77		$1,020.9769	$1,020.98	$1,021.00	$1,020.90