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	$91.75	12.135%	$102.8839	$102.88	$102.90	$102.90
Purchase #2	$79.90	7.499%	$85.8917	$85.89	$85.90	$85.90
Purchase #3	$72.36	11.649%	$80.7892	$80.79	$80.80	$80.80
Purchase #4	$106.25	11.764%	$118.7493	$118.75	$118.75	$118.70
Purchase #5	$141.86	9.529%	$155.3778	$155.38	$155.40	$155.40
Purchase #6	$245.85	5.806%	$260.1241	$260.12	$260.10	$260.10
Purchase #7	$64.32	11.365%	$71.63	$71.63	$71.65	$71.60
7 purchase totals =	$802.29		$875.4460	$875.44	$875.50	$875.40