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	$157.84	8.749%	$171.6494	$171.65	$171.65	$171.60
Purchase #2	$75.38	8.240%	$81.5913	$81.59	$81.60	$81.60
Purchase #3	$142.36	3.402%	$147.2031	$147.20	$147.20	$147.20
Purchase #4	$101.63	9.362%	$111.1446	$111.14	$111.15	$111.10
Purchase #5	$103.89	6.708%	$110.8589	$110.86	$110.85	$110.90
Purchase #6	$78.76	13.294%	$89.2304	$89.23	$89.25	$89.20
Purchase #7	$54.50	8.826%	$59.3102	$59.31	$59.30	$59.30
7 purchase totals =	$714.36		$770.9879	$770.98	$771.00	$770.90