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	$107.48	4.508%	$112.3252	$112.33	$112.35	$112.30
Purchase #2	$245.30	11.346%	$273.1317	$273.13	$273.15	$273.10
Purchase #3	$134.83	6.476%	$143.5616	$143.56	$143.55	$143.60
Purchase #4	$191.56	11.628%	$213.8346	$213.83	$213.85	$213.80
Purchase #5	$135.86	5.340%	$143.1149	$143.11	$143.10	$143.10
Purchase #6	$16.38	6.780%	$17.4906	$17.49	$17.50	$17.50
Purchase #7	$191.40	4.410%	$199.8407	$199.84	$199.85	$199.80
7 purchase totals =	$1,022.81		$1,103.2993	$1,103.29	$1,103.35	$1,103.20