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	$26.36	6.382%	$28.0423	$28.04	$28.05	$28.00
Purchase #2	$49.86	7.112%	$53.406	$53.41	$53.40	$53.40
Purchase #3	$235.40	8.814%	$256.1482	$256.15	$256.15	$256.10
Purchase #4	$81.39	12.194%	$91.3147	$91.31	$91.30	$91.30
Purchase #5	$108.96	13.270%	$123.419	$123.42	$123.40	$123.40
Purchase #6	$169.37	13.653%	$192.4941	$192.49	$192.50	$192.50
Purchase #7	$98.34	12.194%	$110.3316	$110.33	$110.35	$110.30
7 purchase totals =	$769.68		$855.1559	$855.15	$855.15	$855.00