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 $243.52   12.663%   $274.3569   $274.36   $274.35   $274.40  
  Purchase #2 $213.62   10.290%   $235.6015   $235.60   $235.60   $235.60  
  Purchase #3 $234.71   3.104%   $241.9954   $242.00   $242.00   $242.00  
  Purchase #4 $28.86   8.356%   $31.2715   $31.27   $31.25   $31.30  
  Purchase #5 $210.53   11.456%   $234.6483   $234.65   $234.65   $234.60  
  Purchase #6 $139.69   8.671%   $151.8025   $151.80   $151.80   $151.80  
  Purchase #7 $137.91   10.470%   $152.3492   $152.35   $152.35   $152.30  
  7 purchase totals = $1,208.84       $1,322.0253   $1,322.03   $1,322.00   $1,322.00