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	$73.30	6.832%	$78.3079	$78.31	$78.30	$78.30
Purchase #2	$237.93	6.474%	$253.3336	$253.33	$253.35	$253.30
Purchase #3	$246.89	3.302%	$255.0423	$255.04	$255.05	$255.00
Purchase #4	$28.83	4.863%	$30.232	$30.23	$30.25	$30.20
Purchase #5	$39.39	3.590%	$40.8041	$40.80	$40.80	$40.80
Purchase #6	$53.75	3.848%	$55.8183	$55.82	$55.80	$55.80
Purchase #7	$189.56	9.654%	$207.8601	$207.86	$207.85	$207.90
7 purchase totals =	$869.65		$921.3983	$921.39	$921.40	$921.30