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	$70.95	6.473%	$75.5426	$75.54	$75.55	$75.50
Purchase #2	$167.44	7.606%	$180.1755	$180.18	$180.20	$180.20
Purchase #3	$120.72	9.122%	$131.7321	$131.73	$131.75	$131.70
Purchase #4	$112.31	9.712%	$123.2175	$123.22	$123.20	$123.20
Purchase #5	$162.50	6.553%	$173.1486	$173.15	$173.15	$173.10
Purchase #6	$241.84	11.717%	$270.1764	$270.18	$270.20	$270.20
Purchase #7	$47.33	7.464%	$50.8627	$50.86	$50.85	$50.90
7 purchase totals =	$923.09		$1,004.8554	$1,004.86	$1,004.90	$1,004.80