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	$130.35	4.596%	$136.3409	$136.34	$136.35	$136.30
Purchase #2	$78.68	4.289%	$82.0546	$82.05	$82.05	$82.10
Purchase #3	$98.53	12.764%	$111.1064	$111.11	$111.10	$111.10
Purchase #4	$119.53	10.808%	$132.4488	$132.45	$132.45	$132.40
Purchase #5	$62.70	10.151%	$69.0647	$69.06	$69.05	$69.10
Purchase #6	$223.73	12.170%	$250.9579	$250.96	$250.95	$251.00
Purchase #7	$185.60	7.551%	$199.6147	$199.61	$199.60	$199.60
7 purchase totals =	$899.12		$981.5880	$981.58	$981.55	$981.60