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	$159.27	10.402%	$175.8373	$175.84	$175.85	$175.80
Purchase #2	$36.46	9.485%	$39.9182	$39.92	$39.90	$39.90
Purchase #3	$229.67	11.427%	$255.9144	$255.91	$255.90	$255.90
Purchase #4	$112.39	4.259%	$117.1767	$117.18	$117.20	$117.20
Purchase #5	$39.86	3.797%	$41.3735	$41.37	$41.35	$41.40
Purchase #6	$80.31	6.632%	$85.6362	$85.64	$85.65	$85.60
Purchase #7	$126.96	3.451%	$131.3414	$131.34	$131.35	$131.30
7 purchase totals =	$784.92		$847.1977	$847.20	$847.20	$847.10