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	$77.97	10.148%	$85.8824	$85.88	$85.90	$85.90
Purchase #2	$212.76	5.194%	$223.8108	$223.81	$223.80	$223.80
Purchase #3	$73.73	13.382%	$83.5965	$83.60	$83.60	$83.60
Purchase #4	$229.52	8.640%	$249.3505	$249.35	$249.35	$249.40
Purchase #5	$141.83	8.104%	$153.3239	$153.32	$153.30	$153.30
Purchase #6	$55.78	3.427%	$57.6916	$57.69	$57.70	$57.70
Purchase #7	$62.61	7.533%	$67.3264	$67.33	$67.35	$67.30
7 purchase totals =	$854.20		$920.9821	$920.98	$921.00	$921.00