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	$73.49	6.601%	$78.3411	$78.34	$78.35	$78.30
Purchase #2	$219.28	8.460%	$237.8311	$237.83	$237.85	$237.80
Purchase #3	$190.51	9.794%	$209.1685	$209.17	$209.15	$209.20
Purchase #4	$183.90	12.699%	$207.2535	$207.25	$207.25	$207.30
Purchase #5	$42.79	6.450%	$45.55	$45.55	$45.55	$45.60
Purchase #6	$151.89	11.110%	$168.765	$168.77	$168.75	$168.80
Purchase #7	$195.33	4.185%	$203.5046	$203.50	$203.50	$203.50
7 purchase totals =	$1,057.19		$1,150.4138	$1,150.41	$1,150.40	$1,150.50