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	$28.86	10.103%	$31.7757	$31.78	$31.80	$31.80
Purchase #2	$30.37	11.428%	$33.8407	$33.84	$33.85	$33.80
Purchase #3	$177.88	3.754%	$184.5576	$184.56	$184.55	$184.60
Purchase #4	$98.58	10.761%	$109.1882	$109.19	$109.20	$109.20
Purchase #5	$125.36	4.596%	$131.1215	$131.12	$131.10	$131.10
Purchase #6	$161.37	6.192%	$171.362	$171.36	$171.35	$171.40
Purchase #7	$212.44	13.401%	$240.9091	$240.91	$240.90	$240.90
7 purchase totals =	$834.86		$902.7548	$902.76	$902.75	$902.80