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	$62.77	13.334%	$71.1398	$71.14	$71.15	$71.10
Purchase #2	$144.66	3.798%	$150.1542	$150.15	$150.15	$150.20
Purchase #3	$55.96	3.571%	$57.9583	$57.96	$57.95	$58.00
Purchase #4	$208.27	7.709%	$224.3255	$224.33	$224.35	$224.30
Purchase #5	$111.99	13.698%	$127.3304	$127.33	$127.35	$127.30
Purchase #6	$131.80	6.233%	$140.0151	$140.02	$140.00	$140.00
Purchase #7	$75.57	6.764%	$80.6816	$80.68	$80.70	$80.70
7 purchase totals =	$791.02		$851.6049	$851.61	$851.65	$851.60