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	$230.49	4.285%	$240.3665	$240.37	$240.35	$240.40
Purchase #2	$99.58	10.130%	$109.6675	$109.67	$109.65	$109.70
Purchase #3	$46.99	11.790%	$52.5301	$52.53	$52.55	$52.50
Purchase #4	$153.49	9.236%	$167.6663	$167.67	$167.65	$167.70
Purchase #5	$64.84	10.344%	$71.547	$71.55	$71.55	$71.50
Purchase #6	$98.40	10.165%	$108.4024	$108.40	$108.40	$108.40
Purchase #7	$97.33	3.557%	$100.792	$100.79	$100.80	$100.80
7 purchase totals =	$791.12		$850.9718	$850.98	$850.95	$851.00