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	$173.56	4.137%	$180.7402	$180.74	$180.75	$180.70
Purchase #2	$236.89	3.474%	$245.1196	$245.12	$245.10	$245.10
Purchase #3	$79.98	12.303%	$89.8199	$89.82	$89.80	$89.80
Purchase #4	$172.53	9.802%	$189.4414	$189.44	$189.45	$189.40
Purchase #5	$27.79	13.448%	$31.5272	$31.53	$31.55	$31.50
Purchase #6	$75.67	13.177%	$85.641	$85.64	$85.65	$85.60
Purchase #7	$91.35	11.757%	$102.09	$102.09	$102.10	$102.10
7 purchase totals =	$857.77		$924.3793	$924.38	$924.40	$924.20