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	$236.48	5.729%	$250.0279	$250.03	$250.05	$250.00
Purchase #2	$90.89	13.327%	$103.0029	$103.00	$103.00	$103.00
Purchase #3	$90.89	13.441%	$103.1065	$103.11	$103.10	$103.10
Purchase #4	$72.50	9.785%	$79.5941	$79.59	$79.60	$79.60
Purchase #5	$124.28	7.220%	$133.253	$133.25	$133.25	$133.30
Purchase #6	$28.65	7.723%	$30.8626	$30.86	$30.85	$30.90
Purchase #7	$119.69	4.297%	$124.8331	$124.83	$124.85	$124.80
7 purchase totals =	$763.38		$824.6801	$824.67	$824.70	$824.70