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	$91.46	12.595%	$102.9794	$102.98	$103.00	$103.00
Purchase #2	$239.48	12.524%	$269.4725	$269.47	$269.45	$269.50
Purchase #3	$134.27	3.356%	$138.7761	$138.78	$138.80	$138.80
Purchase #4	$145.53	3.292%	$150.3208	$150.32	$150.30	$150.30
Purchase #5	$154.53	3.113%	$159.3405	$159.34	$159.35	$159.30
Purchase #6	$124.47	13.858%	$141.7191	$141.72	$141.70	$141.70
Purchase #7	$133.87	12.736%	$150.9197	$150.92	$150.90	$150.90
7 purchase totals =	$1,023.61		$1,113.5281	$1,113.53	$1,113.50	$1,113.50