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	$79.39	12.409%	$89.2415	$89.24	$89.25	$89.20
Purchase #2	$212.54	9.794%	$233.3562	$233.36	$233.35	$233.40
Purchase #3	$189.87	6.659%	$202.5134	$202.51	$202.50	$202.50
Purchase #4	$154.99	3.163%	$159.8923	$159.89	$159.90	$159.90
Purchase #5	$40.66	11.745%	$45.4355	$45.44	$45.45	$45.40
Purchase #6	$194.59	11.464%	$216.8978	$216.90	$216.90	$216.90
Purchase #7	$100.90	3.121%	$104.0491	$104.05	$104.05	$104.00
7 purchase totals =	$972.94		$1,051.3858	$1,051.39	$1,051.40	$1,051.30