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	$45.61	11.565%	$50.8848	$50.88	$50.90	$50.90
Purchase #2	$181.59	10.400%	$200.4754	$200.48	$200.50	$200.50
Purchase #3	$169.97	12.417%	$191.0752	$191.08	$191.10	$191.10
Purchase #4	$192.95	12.676%	$217.4083	$217.41	$217.40	$217.40
Purchase #5	$33.55	6.858%	$35.8509	$35.85	$35.85	$35.90
Purchase #6	$42.84	10.540%	$47.3553	$47.36	$47.35	$47.40
Purchase #7	$113.65	4.544%	$118.8143	$118.81	$118.80	$118.80
7 purchase totals =	$780.16		$861.8642	$861.87	$861.90	$862.00