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	$170.63	10.661%	$188.8209	$188.82	$188.80	$188.80
Purchase #2	$53.41	13.371%	$60.5515	$60.55	$60.55	$60.60
Purchase #3	$50.89	13.498%	$57.7591	$57.76	$57.75	$57.80
Purchase #4	$215.97	9.206%	$235.8522	$235.85	$235.85	$235.90
Purchase #5	$25.91	11.563%	$28.906	$28.91	$28.90	$28.90
Purchase #6	$168.33	10.290%	$185.6512	$185.65	$185.65	$185.70
Purchase #7	$88.96	12.700%	$100.2579	$100.26	$100.25	$100.30
7 purchase totals =	$774.10		$857.7988	$857.80	$857.75	$858.00