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	$36.99	10.471%	$40.8632	$40.86	$40.85	$40.90
Purchase #2	$53.29	5.803%	$56.3824	$56.38	$56.40	$56.40
Purchase #3	$168.30	10.383%	$185.7746	$185.77	$185.75	$185.80
Purchase #4	$229.46	7.102%	$245.7562	$245.76	$245.75	$245.80
Purchase #5	$93.73	7.212%	$100.4898	$100.49	$100.50	$100.50
Purchase #6	$219.37	10.780%	$243.0181	$243.02	$243.00	$243.00
Purchase #7	$47.92	9.645%	$52.5419	$52.54	$52.55	$52.50
7 purchase totals =	$849.06		$924.8262	$924.82	$924.80	$924.90