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	$99.82	12.257%	$112.0549	$112.05	$112.05	$112.10
Purchase #2	$80.76	10.182%	$88.983	$88.98	$89.00	$89.00
Purchase #3	$64.96	10.673%	$71.8932	$71.89	$71.90	$71.90
Purchase #4	$90.83	9.850%	$99.7768	$99.78	$99.80	$99.80
Purchase #5	$107.28	11.550%	$119.6708	$119.67	$119.65	$119.70
Purchase #6	$53.84	3.740%	$55.8536	$55.85	$55.85	$55.90
Purchase #7	$73.52	12.110%	$82.4233	$82.42	$82.40	$82.40
7 purchase totals =	$571.01		$630.6556	$630.64	$630.65	$630.80