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	$82.30	9.271%	$89.93	$89.93	$89.95	$89.90
Purchase #2	$175.80	7.441%	$188.8813	$188.88	$188.90	$188.90
Purchase #3	$81.60	6.786%	$87.1374	$87.14	$87.15	$87.10
Purchase #4	$171.48	13.222%	$194.1531	$194.15	$194.15	$194.20
Purchase #5	$48.89	10.855%	$54.197	$54.20	$54.20	$54.20
Purchase #6	$94.54	4.742%	$99.0231	$99.02	$99.00	$99.00
Purchase #7	$240.98	9.563%	$264.0249	$264.02	$264.00	$264.00
7 purchase totals =	$895.59		$977.3468	$977.34	$977.35	$977.30