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	$70.67	3.190%	$72.9244	$72.92	$72.90	$72.90
Purchase #2	$147.76	7.804%	$159.2912	$159.29	$159.30	$159.30
Purchase #3	$23.29	13.405%	$26.412	$26.41	$26.40	$26.40
Purchase #4	$69.75	12.631%	$78.5601	$78.56	$78.55	$78.60
Purchase #5	$227.33	6.638%	$242.4202	$242.42	$242.40	$242.40
Purchase #6	$167.72	6.210%	$178.1354	$178.14	$178.15	$178.10
Purchase #7	$57.81	9.236%	$63.1493	$63.15	$63.15	$63.10
7 purchase totals =	$764.33		$820.8926	$820.89	$820.85	$820.80