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	$67.49	11.281%	$75.1035	$75.10	$75.10	$75.10
Purchase #2	$151.94	10.492%	$167.8815	$167.88	$167.90	$167.90
Purchase #3	$92.37	10.199%	$101.7908	$101.79	$101.80	$101.80
Purchase #4	$65.95	9.623%	$72.2964	$72.30	$72.30	$72.30
Purchase #5	$79.35	12.813%	$89.5171	$89.52	$89.50	$89.50
Purchase #6	$242.77	3.307%	$250.7984	$250.80	$250.80	$250.80
Purchase #7	$106.37	12.658%	$119.8343	$119.83	$119.85	$119.80
7 purchase totals =	$806.24		$877.2220	$877.22	$877.25	$877.20