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	$180.72	4.498%	$188.8488	$188.85	$188.85	$188.80
Purchase #2	$83.95	7.414%	$90.1741	$90.17	$90.15	$90.20
Purchase #3	$168.29	9.409%	$184.1244	$184.12	$184.10	$184.10
Purchase #4	$59.44	6.483%	$63.2935	$63.29	$63.30	$63.30
Purchase #5	$194.50	8.437%	$210.91	$210.91	$210.90	$210.90
Purchase #6	$73.68	12.298%	$82.7412	$82.74	$82.75	$82.70
Purchase #7	$182.40	9.441%	$199.6204	$199.62	$199.60	$199.60
7 purchase totals =	$942.98		$1,019.7124	$1,019.70	$1,019.65	$1,019.60