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	$8.97	10.455%	$9.9078	$9.91	$9.90	$9.90
Purchase #2	$95.42	4.588%	$99.7979	$99.80	$99.80	$99.80
Purchase #3	$110.25	13.266%	$124.8758	$124.88	$124.90	$124.90
Purchase #4	$176.36	11.413%	$196.488	$196.49	$196.50	$196.50
Purchase #5	$96.67	3.179%	$99.7431	$99.74	$99.75	$99.70
Purchase #6	$59.51	3.686%	$61.7035	$61.70	$61.70	$61.70
Purchase #7	$98.51	3.252%	$101.7135	$101.71	$101.70	$101.70
7 purchase totals =	$645.69		$694.2296	$694.23	$694.25	$694.20