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	11.148%	$78.5483	$78.55	$78.55	$78.50
Purchase #2	$160.42	3.357%	$165.8053	$165.81	$165.80	$165.80
Purchase #3	$215.86	12.617%	$243.0951	$243.10	$243.10	$243.10
Purchase #4	$121.46	10.521%	$134.2388	$134.24	$134.25	$134.20
Purchase #5	$227.82	13.229%	$257.9583	$257.96	$257.95	$258.00
Purchase #6	$60.80	10.544%	$67.2108	$67.21	$67.20	$67.20
Purchase #7	$141.98	8.299%	$153.7629	$153.76	$153.75	$153.80
7 purchase totals =	$999.01		$1,100.6195	$1,100.63	$1,100.60	$1,100.60