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	$165.76	5.279%	$174.5105	$174.51	$174.50	$174.50
Purchase #2	$69.51	12.851%	$78.4427	$78.44	$78.45	$78.40
Purchase #3	$88.80	8.499%	$96.3471	$96.35	$96.35	$96.30
Purchase #4	$142.87	7.627%	$153.7667	$153.77	$153.75	$153.80
Purchase #5	$131.55	12.444%	$147.9201	$147.92	$147.90	$147.90
Purchase #6	$147.84	12.759%	$166.7029	$166.70	$166.70	$166.70
Purchase #7	$50.36	5.708%	$53.2345	$53.23	$53.25	$53.20
7 purchase totals =	$796.69		$870.9245	$870.92	$870.90	$870.80