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	$28.34	3.832%	$29.426	$29.43	$29.45	$29.40
Purchase #2	$76.81	10.760%	$85.0748	$85.07	$85.05	$85.10
Purchase #3	$250.73	7.213%	$268.8152	$268.82	$268.80	$268.80
Purchase #4	$80.76	6.442%	$85.9626	$85.96	$85.95	$86.00
Purchase #5	$177.27	4.859%	$185.8835	$185.88	$185.90	$185.90
Purchase #6	$64.64	7.813%	$69.6903	$69.69	$69.70	$69.70
Purchase #7	$145.28	7.643%	$156.3838	$156.38	$156.40	$156.40
7 purchase totals =	$823.83		$881.2362	$881.23	$881.25	$881.30