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	$80.77	9.317%	$88.2953	$88.30	$88.30	$88.30
Purchase #2	$176.26	3.848%	$183.0425	$183.04	$183.05	$183.00
Purchase #3	$155.87	10.557%	$172.3252	$172.33	$172.35	$172.30
Purchase #4	$128.46	7.513%	$138.1112	$138.11	$138.10	$138.10
Purchase #5	$48.67	10.753%	$53.9035	$53.90	$53.90	$53.90
Purchase #6	$45.83	4.484%	$47.885	$47.89	$47.90	$47.90
Purchase #7	$247.73	11.134%	$275.3123	$275.31	$275.30	$275.30
7 purchase totals =	$883.59		$958.8750	$958.88	$958.90	$958.80