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	$142.27	5.803%	$150.5259	$150.53	$150.55	$150.50
Purchase #2	$38.56	7.117%	$41.3043	$41.30	$41.30	$41.30
Purchase #3	$140.73	6.515%	$149.8986	$149.90	$149.90	$149.90
Purchase #4	$106.67	7.126%	$114.2713	$114.27	$114.25	$114.30
Purchase #5	$37.88	5.371%	$39.9145	$39.91	$39.90	$39.90
Purchase #6	$91.71	8.832%	$99.8098	$99.81	$99.80	$99.80
Purchase #7	$67.91	7.586%	$73.0617	$73.06	$73.05	$73.10
7 purchase totals =	$625.73		$668.7861	$668.78	$668.75	$668.80