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	$80.81	10.625%	$89.3961	$89.40	$89.40	$89.40
Purchase #2	$239.60	5.798%	$253.492	$253.49	$253.50	$253.50
Purchase #3	$245.72	7.814%	$264.9206	$264.92	$264.90	$264.90
Purchase #4	$170.33	9.142%	$185.9016	$185.90	$185.90	$185.90
Purchase #5	$225.97	7.104%	$242.0229	$242.02	$242.00	$242.00
Purchase #6	$146.54	13.680%	$166.5867	$166.59	$166.60	$166.60
Purchase #7	$125.33	12.152%	$140.5601	$140.56	$140.55	$140.60
7 purchase totals =	$1,234.30		$1,342.8800	$1,342.88	$1,342.85	$1,342.90