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	$238.75	6.443%	$254.1327	$254.13	$254.15	$254.10
Purchase #2	$35.85	6.836%	$38.3007	$38.30	$38.30	$38.30
Purchase #3	$33.93	3.437%	$35.0962	$35.10	$35.10	$35.10
Purchase #4	$199.74	11.514%	$222.7381	$222.74	$222.75	$222.70
Purchase #5	$136.39	10.303%	$150.4423	$150.44	$150.45	$150.40
Purchase #6	$54.25	8.238%	$58.7191	$58.72	$58.70	$58.70
Purchase #7	$245.92	7.304%	$263.882	$263.88	$263.90	$263.90
7 purchase totals =	$944.83		$1,023.3111	$1,023.31	$1,023.35	$1,023.20