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	$12.31	6.471%	$13.1066	$13.11	$13.10	$13.10
Purchase #2	$33.32	6.280%	$35.4125	$35.41	$35.40	$35.40
Purchase #3	$11.80	10.229%	$13.007	$13.01	$13.00	$13.00
Purchase #4	$205.60	13.791%	$233.9543	$233.95	$233.95	$234.00
Purchase #5	$51.53	3.647%	$53.4093	$53.41	$53.40	$53.40
Purchase #6	$92.40	3.426%	$95.5656	$95.57	$95.55	$95.60
Purchase #7	$64.46	11.543%	$71.9006	$71.90	$71.90	$71.90
7 purchase totals =	$471.42		$516.3559	$516.36	$516.30	$516.40