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	$82.34	5.499%	$86.8679	$86.87	$86.85	$86.90
Purchase #2	$122.57	10.457%	$135.3871	$135.39	$135.40	$135.40
Purchase #3	$88.39	7.293%	$94.8363	$94.84	$94.85	$94.80
Purchase #4	$70.71	11.221%	$78.6444	$78.64	$78.65	$78.60
Purchase #5	$240.43	4.117%	$250.3285	$250.33	$250.35	$250.30
Purchase #6	$44.63	12.712%	$50.3034	$50.30	$50.30	$50.30
Purchase #7	$130.61	9.423%	$142.9174	$142.92	$142.90	$142.90
7 purchase totals =	$779.68		$839.2850	$839.29	$839.30	$839.20