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	$111.29	12.106%	$124.7628	$124.76	$124.75	$124.80
Purchase #2	$75.26	9.464%	$82.3826	$82.38	$82.40	$82.40
Purchase #3	$206.37	12.474%	$232.1126	$232.11	$232.10	$232.10
Purchase #4	$65.92	10.718%	$72.9853	$72.99	$73.00	$73.00
Purchase #5	$39.81	7.799%	$42.9148	$42.91	$42.90	$42.90
Purchase #6	$139.89	13.868%	$159.2899	$159.29	$159.30	$159.30
Purchase #7	$84.39	7.703%	$90.8906	$90.89	$90.90	$90.90
7 purchase totals =	$722.93		$805.3386	$805.33	$805.35	$805.40