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	$179.78	7.842%	$193.8783	$193.88	$193.90	$193.90
Purchase #2	$53.51	11.243%	$59.5261	$59.53	$59.55	$59.50
Purchase #3	$129.57	5.642%	$136.8803	$136.88	$136.90	$136.90
Purchase #4	$36.74	10.247%	$40.5047	$40.50	$40.50	$40.50
Purchase #5	$215.51	6.683%	$229.9125	$229.91	$229.90	$229.90
Purchase #6	$189.37	10.666%	$209.5682	$209.57	$209.55	$209.60
Purchase #7	$197.72	13.270%	$223.9574	$223.96	$223.95	$224.00
7 purchase totals =	$1,002.20		$1,094.2275	$1,094.23	$1,094.25	$1,094.30