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	$139.41	12.548%	$156.9032	$156.90	$156.90	$156.90
Purchase #2	$59.67	4.275%	$62.2209	$62.22	$62.20	$62.20
Purchase #3	$82.46	11.354%	$91.8225	$91.82	$91.80	$91.80
Purchase #4	$212.36	4.181%	$221.2388	$221.24	$221.25	$221.20
Purchase #5	$240.69	5.231%	$253.2805	$253.28	$253.30	$253.30
Purchase #6	$53.68	6.544%	$57.1928	$57.19	$57.20	$57.20
Purchase #7	$48.33	7.364%	$51.889	$51.89	$51.90	$51.90
7 purchase totals =	$836.60		$894.5477	$894.54	$894.55	$894.50