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	$85.96	9.726%	$94.3205	$94.32	$94.30	$94.30
Purchase #2	$222.91	11.754%	$249.1108	$249.11	$249.10	$249.10
Purchase #3	$218.54	7.609%	$235.1687	$235.17	$235.15	$235.20
Purchase #4	$77.40	10.142%	$85.2499	$85.25	$85.25	$85.20
Purchase #5	$134.34	12.574%	$151.2319	$151.23	$151.25	$151.20
Purchase #6	$95.46	11.620%	$106.5525	$106.55	$106.55	$106.60
Purchase #7	$89.69	4.625%	$93.8382	$93.84	$93.85	$93.80
7 purchase totals =	$924.30		$1,015.4725	$1,015.47	$1,015.45	$1,015.40