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	$186.48	5.374%	$196.5014	$196.50	$196.50	$196.50
Purchase #2	$89.34	12.286%	$100.3163	$100.32	$100.30	$100.30
Purchase #3	$177.66	5.270%	$187.0227	$187.02	$187.00	$187.00
Purchase #4	$36.73	6.785%	$39.2221	$39.22	$39.20	$39.20
Purchase #5	$156.82	10.530%	$173.3331	$173.33	$173.35	$173.30
Purchase #6	$28.46	8.367%	$30.8412	$30.84	$30.85	$30.80
Purchase #7	$200.82	4.844%	$210.5477	$210.55	$210.55	$210.50
7 purchase totals =	$876.31		$937.7845	$937.78	$937.75	$937.60