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	$165.65	13.592%	$188.1651	$188.17	$188.15	$188.20
Purchase #2	$123.44	6.762%	$131.787	$131.79	$131.80	$131.80
Purchase #3	$40.39	13.382%	$45.795	$45.80	$45.80	$45.80
Purchase #4	$119.69	3.862%	$124.3124	$124.31	$124.30	$124.30
Purchase #5	$92.63	3.215%	$95.6081	$95.61	$95.60	$95.60
Purchase #6	$147.85	13.223%	$167.4002	$167.40	$167.40	$167.40
Purchase #7	$90.56	9.285%	$98.9685	$98.97	$98.95	$99.00
7 purchase totals =	$780.21		$852.0363	$852.05	$852.00	$852.10