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	$91.97	12.781%	$103.7247	$103.72	$103.70	$103.70
Purchase #2	$236.32	9.497%	$258.7633	$258.76	$258.75	$258.80
Purchase #3	$186.33	13.121%	$210.7784	$210.78	$210.80	$210.80
Purchase #4	$49.42	7.529%	$53.1408	$53.14	$53.15	$53.10
Purchase #5	$26.81	6.140%	$28.4561	$28.46	$28.45	$28.50
Purchase #6	$162.63	5.353%	$171.3356	$171.34	$171.35	$171.30
Purchase #7	$92.56	6.211%	$98.3089	$98.31	$98.30	$98.30
7 purchase totals =	$846.04		$924.5078	$924.51	$924.50	$924.50