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	$125.52	12.847%	$141.6456	$141.65	$141.65	$141.60
Purchase #2	$93.68	6.444%	$99.7167	$99.72	$99.70	$99.70
Purchase #3	$125.63	8.258%	$136.0045	$136.00	$136.00	$136.00
Purchase #4	$78.81	4.793%	$82.5874	$82.59	$82.60	$82.60
Purchase #5	$235.66	4.104%	$245.3315	$245.33	$245.35	$245.30
Purchase #6	$82.47	8.437%	$89.428	$89.43	$89.45	$89.40
Purchase #7	$25.30	12.689%	$28.5103	$28.51	$28.50	$28.50
7 purchase totals =	$767.07		$823.2240	$823.23	$823.25	$823.10