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	$218.59	4.529%	$228.4899	$228.49	$228.50	$228.50
Purchase #2	$116.44	10.793%	$129.0074	$129.01	$129.00	$129.00
Purchase #3	$90.70	11.540%	$101.1668	$101.17	$101.15	$101.20
Purchase #4	$11.33	10.349%	$12.5025	$12.50	$12.50	$12.50
Purchase #5	$41.70	5.371%	$43.9397	$43.94	$43.95	$43.90
Purchase #6	$209.48	6.503%	$223.1025	$223.10	$223.10	$223.10
Purchase #7	$38.54	6.148%	$40.9094	$40.91	$40.90	$40.90
7 purchase totals =	$726.78		$779.1182	$779.12	$779.10	$779.10