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	$123.57	3.631%	$128.0568	$128.06	$128.05	$128.10
Purchase #2	$189.44	5.164%	$199.2227	$199.22	$199.20	$199.20
Purchase #3	$98.53	6.338%	$104.7748	$104.77	$104.75	$104.80
Purchase #4	$35.50	13.783%	$40.393	$40.39	$40.40	$40.40
Purchase #5	$198.35	5.505%	$209.2692	$209.27	$209.25	$209.30
Purchase #6	$173.38	13.645%	$197.0377	$197.04	$197.05	$197.00
Purchase #7	$208.58	6.460%	$222.0543	$222.05	$222.05	$222.10
7 purchase totals =	$1,027.35		$1,100.8085	$1,100.80	$1,100.75	$1,100.90