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	$25.28	10.428%	$27.9162	$27.92	$27.90	$27.90
Purchase #2	$156.46	3.609%	$162.1066	$162.11	$162.10	$162.10
Purchase #3	$19.85	7.179%	$21.275	$21.28	$21.30	$21.30
Purchase #4	$64.90	11.435%	$72.3213	$72.32	$72.30	$72.30
Purchase #5	$243.89	9.765%	$267.7059	$267.71	$267.70	$267.70
Purchase #6	$249.51	8.344%	$270.3291	$270.33	$270.35	$270.30
Purchase #7	$59.71	3.603%	$61.8614	$61.86	$61.85	$61.90
7 purchase totals =	$819.60		$883.5155	$883.53	$883.50	$883.50