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	$68.90	13.398%	$78.1312	$78.13	$78.15	$78.10
Purchase #2	$92.34	10.607%	$102.1345	$102.13	$102.15	$102.10
Purchase #3	$243.38	10.617%	$269.2197	$269.22	$269.20	$269.20
Purchase #4	$39.83	6.188%	$42.2947	$42.29	$42.30	$42.30
Purchase #5	$6.58	8.534%	$7.1415	$7.14	$7.15	$7.10
Purchase #6	$205.57	6.553%	$219.041	$219.04	$219.05	$219.00
Purchase #7	$47.48	12.834%	$53.5736	$53.57	$53.55	$53.60
7 purchase totals =	$704.08		$771.5362	$771.52	$771.55	$771.40