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	$175.66	9.862%	$192.9836	$192.98	$193.00	$193.00
Purchase #2	$240.97	11.138%	$267.8092	$267.81	$267.80	$267.80
Purchase #3	$53.81	10.329%	$59.368	$59.37	$59.35	$59.40
Purchase #4	$186.84	12.457%	$210.1147	$210.11	$210.10	$210.10
Purchase #5	$40.82	4.649%	$42.7177	$42.72	$42.70	$42.70
Purchase #6	$6.76	9.639%	$7.4116	$7.41	$7.40	$7.40
Purchase #7	$93.89	5.527%	$99.0793	$99.08	$99.10	$99.10
7 purchase totals =	$798.75		$879.4841	$879.48	$879.45	$879.50