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	$171.62	5.288%	$180.6953	$180.70	$180.70	$180.70
Purchase #2	$100.48	9.456%	$109.9814	$109.98	$110.00	$110.00
Purchase #3	$74.90	6.659%	$79.8876	$79.89	$79.90	$79.90
Purchase #4	$6.36	10.629%	$7.036	$7.04	$7.05	$7.00
Purchase #5	$69.43	13.648%	$78.9058	$78.91	$78.90	$78.90
Purchase #6	$164.96	12.628%	$185.7911	$185.79	$185.80	$185.80
Purchase #7	$22.51	11.743%	$25.1533	$25.15	$25.15	$25.20
7 purchase totals =	$610.26		$667.4505	$667.46	$667.50	$667.50