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	$39.86	5.324%	$41.9821	$41.98	$42.00	$42.00
Purchase #2	$90.57	8.372%	$98.1525	$98.15	$98.15	$98.20
Purchase #3	$123.34	6.689%	$131.5902	$131.59	$131.60	$131.60
Purchase #4	$92.48	7.607%	$99.515	$99.52	$99.50	$99.50
Purchase #5	$189.96	12.313%	$213.3498	$213.35	$213.35	$213.30
Purchase #6	$29.72	4.770%	$31.1376	$31.14	$31.15	$31.10
Purchase #7	$194.41	11.674%	$217.1054	$217.11	$217.10	$217.10
7 purchase totals =	$760.34		$832.8326	$832.84	$832.85	$832.80