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	8.833%	$99.5387	$99.54	$99.55	$99.50
Purchase #2	$190.33	10.479%	$210.2747	$210.27	$210.25	$210.30
Purchase #3	$209.78	11.279%	$233.4411	$233.44	$233.45	$233.40
Purchase #4	$120.56	12.192%	$135.2587	$135.26	$135.25	$135.30
Purchase #5	$29.76	10.112%	$32.7693	$32.77	$32.75	$32.80
Purchase #6	$97.98	12.804%	$110.5254	$110.53	$110.55	$110.50
Purchase #7	$182.61	4.458%	$190.7508	$190.75	$190.75	$190.80
7 purchase totals =	$922.48		$1,012.5587	$1,012.56	$1,012.55	$1,012.60