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	$78.62	5.577%	$83.0046	$83.00	$83.00	$83.00
Purchase #2	$153.50	7.160%	$164.4906	$164.49	$164.50	$164.50
Purchase #3	$198.88	13.801%	$226.3274	$226.33	$226.35	$226.30
Purchase #4	$96.57	4.311%	$100.7331	$100.73	$100.75	$100.70
Purchase #5	$169.36	7.530%	$182.1128	$182.11	$182.10	$182.10
Purchase #6	$104.64	7.479%	$112.466	$112.47	$112.45	$112.50
Purchase #7	$54.54	9.204%	$59.5599	$59.56	$59.55	$59.60
7 purchase totals =	$856.11		$928.6944	$928.69	$928.70	$928.70