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	$93.57	6.563%	$99.711	$99.71	$99.70	$99.70
Purchase #2	$126.74	5.192%	$133.3203	$133.32	$133.30	$133.30
Purchase #3	$156.48	7.572%	$168.3287	$168.33	$168.35	$168.30
Purchase #4	$244.42	10.803%	$270.8247	$270.82	$270.80	$270.80
Purchase #5	$184.62	6.496%	$196.6129	$196.61	$196.60	$196.60
Purchase #6	$216.63	12.417%	$243.5289	$243.53	$243.55	$243.50
Purchase #7	$86.86	11.442%	$96.7985	$96.80	$96.80	$96.80
7 purchase totals =	$1,109.32		$1,209.1250	$1,209.12	$1,209.10	$1,209.00