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	$108.41	13.817%	$123.389	$123.39	$123.40	$123.40
Purchase #2	$22.53	12.373%	$25.3176	$25.32	$25.30	$25.30
Purchase #3	$131.90	11.704%	$147.3376	$147.34	$147.35	$147.30
Purchase #4	$94.93	11.775%	$106.108	$106.11	$106.10	$106.10
Purchase #5	$136.71	5.352%	$144.0267	$144.03	$144.05	$144.00
Purchase #6	$86.97	12.813%	$98.1135	$98.11	$98.10	$98.10
Purchase #7	$15.33	3.536%	$15.8721	$15.87	$15.85	$15.90
7 purchase totals =	$596.78		$660.1645	$660.17	$660.15	$660.10