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	$27.60	3.515%	$28.5701	$28.57	$28.55	$28.60
Purchase #2	$101.76	8.427%	$110.3353	$110.34	$110.35	$110.30
Purchase #3	$134.73	12.859%	$152.0549	$152.05	$152.05	$152.10
Purchase #4	$127.83	12.166%	$143.3818	$143.38	$143.40	$143.40
Purchase #5	$198.78	11.276%	$221.1944	$221.19	$221.20	$221.20
Purchase #6	$82.32	8.858%	$89.6119	$89.61	$89.60	$89.60
Purchase #7	$42.46	10.562%	$46.9446	$46.94	$46.95	$46.90
7 purchase totals =	$715.48		$792.0930	$792.08	$792.10	$792.10