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	$50.73	6.832%	$54.1959	$54.20	$54.20	$54.20
Purchase #2	$72.98	7.337%	$78.3345	$78.33	$78.35	$78.30
Purchase #3	$227.81	6.790%	$243.2783	$243.28	$243.30	$243.30
Purchase #4	$211.91	7.543%	$227.8944	$227.89	$227.90	$227.90
Purchase #5	$243.56	5.182%	$256.1813	$256.18	$256.20	$256.20
Purchase #6	$116.62	11.793%	$130.373	$130.37	$130.35	$130.40
Purchase #7	$225.71	6.460%	$240.2909	$240.29	$240.30	$240.30
7 purchase totals =	$1,149.32		$1,230.5483	$1,230.54	$1,230.60	$1,230.60