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	$12.48	6.665%	$13.3118	$13.31	$13.30	$13.30
Purchase #2	$110.56	6.118%	$117.3241	$117.32	$117.30	$117.30
Purchase #3	$127.65	11.391%	$142.1906	$142.19	$142.20	$142.20
Purchase #4	$90.41	6.666%	$96.4367	$96.44	$96.45	$96.40
Purchase #5	$34.69	3.528%	$35.9139	$35.91	$35.90	$35.90
Purchase #6	$138.72	3.656%	$143.7916	$143.79	$143.80	$143.80
Purchase #7	$229.40	6.330%	$243.921	$243.92	$243.90	$243.90
7 purchase totals =	$743.91		$792.8897	$792.88	$792.85	$792.80