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	$81.31	9.611%	$89.1247	$89.12	$89.10	$89.10
Purchase #2	$140.34	13.334%	$159.0529	$159.05	$159.05	$159.10
Purchase #3	$77.77	6.685%	$82.9689	$82.97	$82.95	$83.00
Purchase #4	$72.96	9.588%	$79.9554	$79.96	$79.95	$80.00
Purchase #5	$99.59	12.523%	$112.0617	$112.06	$112.05	$112.10
Purchase #6	$194.99	7.529%	$209.6708	$209.67	$209.65	$209.70
Purchase #7	$29.74	12.586%	$33.4831	$33.48	$33.50	$33.50
7 purchase totals =	$696.70		$766.3175	$766.31	$766.25	$766.50