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	$30.56	6.574%	$32.569	$32.57	$32.55	$32.60
Purchase #2	$56.98	4.180%	$59.3618	$59.36	$59.35	$59.40
Purchase #3	$19.95	7.424%	$21.4311	$21.43	$21.45	$21.40
Purchase #4	$21.30	3.295%	$22.0018	$22.00	$22.00	$22.00
Purchase #5	$28.68	13.459%	$32.54	$32.54	$32.55	$32.50
Purchase #6	$117.53	6.359%	$125.0037	$125.00	$125.00	$125.00
Purchase #7	$94.33	11.746%	$105.41	$105.41	$105.40	$105.40
7 purchase totals =	$369.33		$398.3174	$398.31	$398.30	$398.30