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	$165.40	9.375%	$180.9063	$180.91	$180.90	$180.90
Purchase #2	$179.38	8.301%	$194.2703	$194.27	$194.25	$194.30
Purchase #3	$99.64	9.629%	$109.2343	$109.23	$109.25	$109.20
Purchase #4	$69.79	12.223%	$78.3204	$78.32	$78.30	$78.30
Purchase #5	$22.97	12.825%	$25.9159	$25.92	$25.90	$25.90
Purchase #6	$104.60	5.771%	$110.6365	$110.64	$110.65	$110.60
Purchase #7	$99.88	9.394%	$109.2627	$109.26	$109.25	$109.30
7 purchase totals =	$741.66		$808.5464	$808.55	$808.50	$808.50