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	$67.49	6.845%	$72.1097	$72.11	$72.10	$72.10
Purchase #2	$151.39	11.191%	$168.3321	$168.33	$168.35	$168.30
Purchase #3	$82.74	13.356%	$93.7908	$93.79	$93.80	$93.80
Purchase #4	$196.44	6.353%	$208.9198	$208.92	$208.90	$208.90
Purchase #5	$62.84	4.347%	$65.5717	$65.57	$65.55	$65.60
Purchase #6	$102.51	7.213%	$109.904	$109.90	$109.90	$109.90
Purchase #7	$214.92	13.110%	$243.096	$243.10	$243.10	$243.10
7 purchase totals =	$878.33		$961.7241	$961.72	$961.70	$961.70