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	$138.31	7.415%	$148.5657	$148.57	$148.55	$148.60
Purchase #2	$34.56	3.738%	$35.8519	$35.85	$35.85	$35.90
Purchase #3	$168.54	12.336%	$189.3311	$189.33	$189.35	$189.30
Purchase #4	$202.53	9.298%	$221.3612	$221.36	$221.35	$221.40
Purchase #5	$104.73	5.830%	$110.8358	$110.84	$110.85	$110.80
Purchase #6	$111.76	4.150%	$116.398	$116.40	$116.40	$116.40
Purchase #7	$113.32	6.317%	$120.4784	$120.48	$120.50	$120.50
7 purchase totals =	$873.75		$942.8221	$942.83	$942.85	$942.90