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	$81.87	10.469%	$90.441	$90.44	$90.45	$90.40
Purchase #2	$136.71	4.396%	$142.7198	$142.72	$142.70	$142.70
Purchase #3	$246.50	7.220%	$264.2973	$264.30	$264.30	$264.30
Purchase #4	$206.84	6.227%	$219.7199	$219.72	$219.70	$219.70
Purchase #5	$64.82	5.420%	$68.3332	$68.33	$68.35	$68.30
Purchase #6	$86.33	3.201%	$89.0934	$89.09	$89.10	$89.10
Purchase #7	$101.88	7.346%	$109.3641	$109.36	$109.35	$109.40
7 purchase totals =	$924.95		$983.9687	$983.96	$983.95	$983.90