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	$82.74	9.135%	$90.2983	$90.30	$90.30	$90.30
Purchase #2	$232.73	9.596%	$255.0628	$255.06	$255.05	$255.10
Purchase #3	$66.88	6.706%	$71.365	$71.37	$71.35	$71.40
Purchase #4	$205.41	6.721%	$219.2156	$219.22	$219.20	$219.20
Purchase #5	$159.36	9.838%	$175.0378	$175.04	$175.05	$175.00
Purchase #6	$31.26	5.215%	$32.8902	$32.89	$32.90	$32.90
Purchase #7	$232.69	5.844%	$246.2884	$246.29	$246.30	$246.30
7 purchase totals =	$1,011.07		$1,090.1581	$1,090.17	$1,090.15	$1,090.20