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	$105.60	9.694%	$115.8369	$115.84	$115.85	$115.80
Purchase #2	$40.42	12.122%	$45.3197	$45.32	$45.30	$45.30
Purchase #3	$249.76	13.316%	$283.018	$283.02	$283.00	$283.00
Purchase #4	$93.70	9.760%	$102.8451	$102.85	$102.85	$102.80
Purchase #5	$75.62	4.187%	$78.7862	$78.79	$78.80	$78.80
Purchase #6	$81.94	11.679%	$91.5098	$91.51	$91.50	$91.50
Purchase #7	$209.38	6.187%	$222.3343	$222.33	$222.35	$222.30
7 purchase totals =	$856.42		$939.6500	$939.66	$939.65	$939.50