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	$27.50	4.568%	$28.7562	$28.76	$28.75	$28.80
Purchase #2	$93.58	6.489%	$99.6524	$99.65	$99.65	$99.70
Purchase #3	$186.40	5.628%	$196.8906	$196.89	$196.90	$196.90
Purchase #4	$215.90	10.290%	$238.1161	$238.12	$238.10	$238.10
Purchase #5	$51.26	3.789%	$53.2022	$53.20	$53.20	$53.20
Purchase #6	$178.82	8.374%	$193.7944	$193.79	$193.80	$193.80
Purchase #7	$169.61	6.345%	$180.3718	$180.37	$180.35	$180.40
7 purchase totals =	$923.07		$990.7837	$990.78	$990.75	$990.90