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	$79.81	12.580%	$89.8501	$89.85	$89.85	$89.90
Purchase #2	$171.59	12.398%	$192.8637	$192.86	$192.85	$192.90
Purchase #3	$19.88	7.379%	$21.3469	$21.35	$21.35	$21.30
Purchase #4	$47.56	12.813%	$53.6539	$53.65	$53.65	$53.70
Purchase #5	$191.47	3.312%	$197.8115	$197.81	$197.80	$197.80
Purchase #6	$37.78	11.443%	$42.1032	$42.10	$42.10	$42.10
Purchase #7	$210.47	9.806%	$231.1087	$231.11	$231.10	$231.10
7 purchase totals =	$758.56		$828.7380	$828.73	$828.70	$828.80