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	$86.50	4.231%	$90.1598	$90.16	$90.15	$90.20
Purchase #2	$31.84	11.775%	$35.5892	$35.59	$35.60	$35.60
Purchase #3	$223.54	10.513%	$247.0408	$247.04	$247.05	$247.00
Purchase #4	$89.84	5.769%	$95.0229	$95.02	$95.00	$95.00
Purchase #5	$229.61	5.594%	$242.4544	$242.45	$242.45	$242.50
Purchase #6	$75.47	5.860%	$79.8925	$79.89	$79.90	$79.90
Purchase #7	$63.50	12.835%	$71.6502	$71.65	$71.65	$71.70
7 purchase totals =	$800.30		$861.8098	$861.80	$861.80	$861.90