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	$140.28	3.787%	$145.5924	$145.59	$145.60	$145.60
Purchase #2	$48.77	7.357%	$52.358	$52.36	$52.35	$52.40
Purchase #3	$247.28	12.378%	$277.8883	$277.89	$277.90	$277.90
Purchase #4	$249.61	6.204%	$265.0958	$265.10	$265.10	$265.10
Purchase #5	$82.74	8.656%	$89.902	$89.90	$89.90	$89.90
Purchase #6	$76.74	11.489%	$85.5567	$85.56	$85.55	$85.60
Purchase #7	$178.46	4.157%	$185.8786	$185.88	$185.90	$185.90
7 purchase totals =	$1,023.88		$1,102.2718	$1,102.28	$1,102.30	$1,102.40