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	$118.66	4.425%	$123.9107	$123.91	$123.90	$123.90
Purchase #2	$233.89	3.698%	$242.5393	$242.54	$242.55	$242.50
Purchase #3	$36.79	7.272%	$39.4654	$39.47	$39.45	$39.50
Purchase #4	$141.31	5.510%	$149.0962	$149.10	$149.10	$149.10
Purchase #5	$246.94	7.405%	$265.2259	$265.23	$265.25	$265.20
Purchase #6	$62.47	13.785%	$71.0815	$71.08	$71.10	$71.10
Purchase #7	$50.89	5.377%	$53.6264	$53.63	$53.65	$53.60
7 purchase totals =	$890.95		$944.9454	$944.96	$945.00	$944.90