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	$115.75	13.333%	$131.1829	$131.18	$131.20	$131.20
Purchase #2	$173.71	9.297%	$189.8598	$189.86	$189.85	$189.90
Purchase #3	$173.55	3.317%	$179.3067	$179.31	$179.30	$179.30
Purchase #4	$116.55	9.733%	$127.8938	$127.89	$127.90	$127.90
Purchase #5	$171.39	6.710%	$182.8903	$182.89	$182.90	$182.90
Purchase #6	$244.93	6.860%	$261.7322	$261.73	$261.75	$261.70
Purchase #7	$106.66	6.216%	$113.29	$113.29	$113.30	$113.30
7 purchase totals =	$1,102.54		$1,186.1557	$1,186.15	$1,186.20	$1,186.20