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	$93.76	13.160%	$106.0988	$106.10	$106.10	$106.10
Purchase #2	$61.34	3.386%	$63.417	$63.42	$63.40	$63.40
Purchase #3	$87.37	5.111%	$91.8355	$91.84	$91.85	$91.80
Purchase #4	$139.26	3.645%	$144.336	$144.34	$144.35	$144.30
Purchase #5	$90.60	4.736%	$94.8908	$94.89	$94.90	$94.90
Purchase #6	$58.93	11.773%	$65.8678	$65.87	$65.85	$65.90
Purchase #7	$196.31	13.850%	$223.4989	$223.50	$223.50	$223.50
7 purchase totals =	$727.57		$789.9448	$789.96	$789.95	$789.90