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	$116.48	6.718%	$124.3051	$124.31	$124.30	$124.30
Purchase #2	$210.56	5.113%	$221.3259	$221.33	$221.35	$221.30
Purchase #3	$174.58	12.807%	$196.9385	$196.94	$196.95	$196.90
Purchase #4	$228.91	11.618%	$255.5048	$255.50	$255.50	$255.50
Purchase #5	$168.71	9.513%	$184.7594	$184.76	$184.75	$184.80
Purchase #6	$184.54	13.565%	$209.5729	$209.57	$209.55	$209.60
Purchase #7	$82.59	12.789%	$93.1524	$93.15	$93.15	$93.20
7 purchase totals =	$1,166.37		$1,285.5590	$1,285.56	$1,285.55	$1,285.60