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	$133.87	4.146%	$139.4203	$139.42	$139.40	$139.40
Purchase #2	$188.33	6.454%	$200.4848	$200.48	$200.50	$200.50
Purchase #3	$157.70	5.624%	$166.569	$166.57	$166.55	$166.60
Purchase #4	$167.75	11.389%	$186.855	$186.86	$186.85	$186.90
Purchase #5	$62.25	12.148%	$69.8121	$69.81	$69.80	$69.80
Purchase #6	$218.79	9.873%	$240.3911	$240.39	$240.40	$240.40
Purchase #7	$150.80	11.506%	$168.151	$168.15	$168.15	$168.20
7 purchase totals =	$1,079.49		$1,171.6833	$1,171.68	$1,171.65	$1,171.80