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	$189.39	4.643%	$198.1834	$198.18	$198.20	$198.20
Purchase #2	$125.82	7.663%	$135.4616	$135.46	$135.45	$135.50
Purchase #3	$79.34	12.648%	$89.3749	$89.37	$89.35	$89.40
Purchase #4	$16.67	11.221%	$18.5405	$18.54	$18.55	$18.50
Purchase #5	$236.33	9.780%	$259.4431	$259.44	$259.45	$259.40
Purchase #6	$216.58	12.576%	$243.8171	$243.82	$243.80	$243.80
Purchase #7	$184.41	11.370%	$205.3774	$205.38	$205.40	$205.40
7 purchase totals =	$1,048.54		$1,150.1980	$1,150.19	$1,150.20	$1,150.20