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	$183.64	3.742%	$190.5118	$190.51	$190.50	$190.50
Purchase #2	$243.45	12.180%	$273.1022	$273.10	$273.10	$273.10
Purchase #3	$63.46	6.691%	$67.7061	$67.71	$67.70	$67.70
Purchase #4	$240.38	7.514%	$258.4422	$258.44	$258.45	$258.40
Purchase #5	$82.30	13.695%	$93.571	$93.57	$93.55	$93.60
Purchase #6	$211.95	12.719%	$238.9079	$238.91	$238.90	$238.90
Purchase #7	$89.41	11.708%	$99.8781	$99.88	$99.90	$99.90
7 purchase totals =	$1,114.59		$1,222.1193	$1,222.12	$1,222.10	$1,222.10