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	$204.25	11.501%	$227.7408	$227.74	$227.75	$227.70
Purchase #2	$244.38	9.690%	$268.0604	$268.06	$268.05	$268.10
Purchase #3	$29.41	12.610%	$33.1186	$33.12	$33.10	$33.10
Purchase #4	$76.28	12.419%	$85.7532	$85.75	$85.75	$85.80
Purchase #5	$233.69	10.456%	$258.1246	$258.12	$258.10	$258.10
Purchase #6	$221.62	9.706%	$243.1304	$243.13	$243.15	$243.10
Purchase #7	$95.78	9.759%	$105.1272	$105.13	$105.15	$105.10
7 purchase totals =	$1,105.41		$1,221.0552	$1,221.05	$1,221.05	$1,221.00