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	$20.54	6.600%	$21.8956	$21.90	$21.90	$21.90
Purchase #2	$166.76	4.703%	$174.6027	$174.60	$174.60	$174.60
Purchase #3	$68.84	5.293%	$72.4837	$72.48	$72.50	$72.50
Purchase #4	$224.40	5.627%	$237.027	$237.03	$237.05	$237.00
Purchase #5	$168.30	12.533%	$189.393	$189.39	$189.40	$189.40
Purchase #6	$233.33	13.443%	$264.6966	$264.70	$264.70	$264.70
Purchase #7	$54.49	8.529%	$59.1375	$59.14	$59.15	$59.10
7 purchase totals =	$936.66		$1,019.2361	$1,019.24	$1,019.30	$1,019.20