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	$72.62	10.821%	$80.4782	$80.48	$80.50	$80.50
Purchase #2	$236.86	11.654%	$264.4637	$264.46	$264.45	$264.50
Purchase #3	$59.71	13.316%	$67.661	$67.66	$67.65	$67.70
Purchase #4	$134.61	3.320%	$139.0791	$139.08	$139.10	$139.10
Purchase #5	$91.51	7.213%	$98.1106	$98.11	$98.10	$98.10
Purchase #6	$247.99	10.788%	$274.7432	$274.74	$274.75	$274.70
Purchase #7	$161.74	5.825%	$171.1614	$171.16	$171.15	$171.20
7 purchase totals =	$1,005.04		$1,095.6972	$1,095.69	$1,095.70	$1,095.80