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	$79.43	9.740%	$87.1665	$87.17	$87.15	$87.20
Purchase #2	$175.62	8.734%	$190.9587	$190.96	$190.95	$191.00
Purchase #3	$25.89	12.549%	$29.1389	$29.14	$29.15	$29.10
Purchase #4	$159.61	7.768%	$172.0085	$172.01	$172.00	$172.00
Purchase #5	$245.94	11.556%	$274.3608	$274.36	$274.35	$274.40
Purchase #6	$242.36	11.562%	$270.3817	$270.38	$270.40	$270.40
Purchase #7	$131.38	8.702%	$142.8127	$142.81	$142.80	$142.80
7 purchase totals =	$1,060.23		$1,166.8278	$1,166.83	$1,166.80	$1,166.90