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	$81.51	12.155%	$91.4175	$91.42	$91.40	$91.40
Purchase #2	$160.67	12.148%	$180.1882	$180.19	$180.20	$180.20
Purchase #3	$129.67	7.375%	$139.2332	$139.23	$139.25	$139.20
Purchase #4	$79.88	8.520%	$86.6858	$86.69	$86.70	$86.70
Purchase #5	$33.36	11.239%	$37.1093	$37.11	$37.10	$37.10
Purchase #6	$235.56	11.852%	$263.4786	$263.48	$263.50	$263.50
Purchase #7	$221.86	10.667%	$245.5258	$245.53	$245.55	$245.50
7 purchase totals =	$942.51		$1,043.6384	$1,043.65	$1,043.70	$1,043.60