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	$129.63	12.361%	$145.6536	$145.65	$145.65	$145.70
Purchase #2	$59.50	3.543%	$61.6081	$61.61	$61.60	$61.60
Purchase #3	$127.57	11.570%	$142.3298	$142.33	$142.35	$142.30
Purchase #4	$53.91	3.661%	$55.8836	$55.88	$55.90	$55.90
Purchase #5	$104.60	10.200%	$115.2692	$115.27	$115.25	$115.30
Purchase #6	$41.79	6.590%	$44.544	$44.54	$44.55	$44.50
Purchase #7	$120.32	3.707%	$124.7803	$124.78	$124.80	$124.80
7 purchase totals =	$637.32		$690.0686	$690.06	$690.10	$690.10