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	$73.32	12.614%	$82.5686	$82.57	$82.55	$82.60
Purchase #2	$106.73	6.152%	$113.296	$113.30	$113.30	$113.30
Purchase #3	$105.60	12.855%	$119.1749	$119.17	$119.15	$119.20
Purchase #4	$165.86	11.471%	$184.8858	$184.89	$184.90	$184.90
Purchase #5	$62.59	13.630%	$71.121	$71.12	$71.10	$71.10
Purchase #6	$143.60	4.468%	$150.016	$150.02	$150.00	$150.00
Purchase #7	$116.53	11.565%	$130.0067	$130.01	$130.00	$130.00
7 purchase totals =	$774.23		$851.0690	$851.08	$851.00	$851.10