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	$173.86	8.768%	$189.104	$189.10	$189.10	$189.10
Purchase #2	$168.73	11.581%	$188.2706	$188.27	$188.25	$188.30
Purchase #3	$33.56	8.686%	$36.475	$36.48	$36.50	$36.50
Purchase #4	$232.67	4.215%	$242.477	$242.48	$242.50	$242.50
Purchase #5	$29.82	6.650%	$31.803	$31.80	$31.80	$31.80
Purchase #6	$125.31	13.729%	$142.5138	$142.51	$142.50	$142.50
Purchase #7	$228.28	9.625%	$250.252	$250.25	$250.25	$250.30
7 purchase totals =	$992.23		$1,080.8954	$1,080.89	$1,080.90	$1,081.00