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	$225.57	3.770%	$234.074	$234.07	$234.05	$234.10
Purchase #2	$79.88	12.513%	$89.8754	$89.88	$89.90	$89.90
Purchase #3	$67.95	7.676%	$73.1658	$73.17	$73.15	$73.20
Purchase #4	$14.63	8.718%	$15.9054	$15.91	$15.90	$15.90
Purchase #5	$28.93	9.550%	$31.6928	$31.69	$31.70	$31.70
Purchase #6	$102.87	11.711%	$114.9171	$114.92	$114.90	$114.90
Purchase #7	$33.93	3.847%	$35.2353	$35.24	$35.25	$35.20
7 purchase totals =	$553.76		$594.8658	$594.88	$594.85	$594.90