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	$83.36	12.599%	$93.8625	$93.86	$93.85	$93.90
Purchase #2	$37.80	6.424%	$40.2283	$40.23	$40.25	$40.20
Purchase #3	$97.50	6.364%	$103.7049	$103.70	$103.70	$103.70
Purchase #4	$78.74	4.363%	$82.1754	$82.18	$82.20	$82.20
Purchase #5	$180.51	9.452%	$197.5718	$197.57	$197.55	$197.60
Purchase #6	$127.38	3.240%	$131.5071	$131.51	$131.50	$131.50
Purchase #7	$35.84	13.831%	$40.797	$40.80	$40.80	$40.80
7 purchase totals =	$641.13		$689.8470	$689.85	$689.85	$689.90