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	$129.73	8.562%	$140.8375	$140.84	$140.85	$140.80
Purchase #2	$151.69	11.164%	$168.6247	$168.62	$168.60	$168.60
Purchase #3	$203.33	9.769%	$223.1933	$223.19	$223.20	$223.20
Purchase #4	$90.97	13.735%	$103.4647	$103.46	$103.45	$103.50
Purchase #5	$71.26	11.259%	$79.2832	$79.28	$79.30	$79.30
Purchase #6	$231.98	7.492%	$249.3599	$249.36	$249.35	$249.40
Purchase #7	$97.88	12.240%	$109.8605	$109.86	$109.85	$109.90
7 purchase totals =	$976.84		$1,074.6238	$1,074.61	$1,074.60	$1,074.70